Being the scrutiniser that I am, I took to scrutinising the scenes in closer detail and originally came to the assumption that BW had screwed up by accidentally spoiling important moments. They've still inadvertently revealed physical details in this trailer, but since then the BW Story Stream has all but revealed that perhaps they weren't accidental spoilers, but more a deliberate tease of stuff to come.
Bear in mind though that for some people this will still be spoiler territory, so if you want to avoid potentially spoiling stuff for yourself, by all means ignore this post and move on.
The trailer features Arcann in a couple of scenes.
First (in a clean shot courtesy of the SWtOR Twitter Account), here he is surrounded by his personal guard
As you can see, he has clearly buffed himself up a notch. His cybernetic arm has (of course) become bulkier and more flashy, his mask now covers more of his face, and his outfit now has splashes of black interwoven amongst the white.
Pretty snazzy, and a good defining shot, since this is the Arcann who players are familiar with. Cybernetic arm, face mask, yup, that's our tyrant!
Then there's this scene later on. No clean shot has been released of this moment, but that's very much a good thing!
This shows three things. First, that Vaylin manages to breach the perimeter of Odessen at some point and that this is most likely her final cinematic moments of life. Second, Senya is alive and well (good!). Third, there's a certain other person there as well, standing alongside his former hated enemy.
It's Arcann! Only this time his outfit is nearly entirely white (including a covering-up of his cybernetic arm), and his face-mask has completely disappeared. I did always wonder whether he actually needed it to live...
Why is Arcann so different between the two shots? Time will tell, but closer inspection of the first screenshot also reveals another detail about that particular Arcann.
His one good eye is yellow. Yellow eyes are, of course, the typical sign of a Dark Force user, and Arcann has been the proud possessor of yellow eyes for his entire time in-game.
How might this reveal the result of various choices? All that is revealed for sure from the second screenshot is that Senya is alive and that Arcann is standing with the Outlander against his sister. Valkorion's spirit can also be seen, so does this mean all that much, really?
Since this moment, Charles Boyd said on the most recent Dev Stream that Senya's mission to heal her son is her main objective, and both of their fates lie in our hands. Essentially, it is now confirmed that Arcann can either end up redeemed or as dark as ever in the main story of this expansion.
Based on the fact that this first Arcann has yellow eyes, it seems clear that this is the Arcann you meet if you try and shoot him down and whose subsequent redemption attempt fails since you gave him no mercy. There is no indication of Senya's fate here, but given Charles Boyd's statement abouth "both of their fates" it is likely that she is no longer alive in this scenario.
Senya is seen in the second image, meaning that in this scenario, Senya survives and has succeeded in redeeming her son. It is thus entirely plausible that Senya's fate is intricately tied to Arcann's own redemption; if she survives, he is redeemed, but if she dies then his redemption fails.
If only there was an image released officially which could show Arcann in some state prior to his appearance in the trailer. Oh, wait, there is!
We can see from this image (once again, courtesy of the official SWtOR Twitter account) that a still bruised and scarred Arcann has been taken to Voss by Senya, which serves as the scene for the first Chapter.
Anyone who knows the planet well will know that one of the most well-known Voss healing practices involves taking the life force from one individual to 'donate it' to another. As notably seen in the Consular storyline, it is more than possible for a strong-willed individual to survive this ritual, and it is often a sign of nobility and/or love if you choose to donate your own life force in the process. This fits Senya's devotion to her son a great deal.
Trying to shoot her down in Chapter XVI might result in a Senya who becomes gradually more weak and fraught, and thus unable to survive such a sacrificial healing ritual, leading Arcann down an even darker path as a result since there is no reason to temper his hatred; his mother was given no mercy, why should he give some to those who refused to be merciful?
If Senya's path is intricately tied to the fate of Arcann as can be implied, then this is clearly how an instant-65 character can define Arcann's character path in their story.
Of course, they never got to try and shoot Senya down, so there is no previously-defined path. With no prior understanding of who Senya is and why she may be worth sparing, I can see many a new player with an instant-65 inadvertently 'creating' the Dark Arcann through butting heads with Senya since all they can see her as is someone trying to help someone that Lana and Theron could be saying needs to be caught.
However, if this decision can be made early into the new expansion for instant characters then it may be possible for characters who went through Fallen Empire to reverse their otherwise 'defined' path. You may try and shoot Arcann down yet still see him redeemed, or allow him to escape and yet still see him decline. There may be four possible paths to the two different apparent outcomes depending on how much content your characters trawled through up until that moment.
The image also confirms that Arcann's eye colour are the most likely indication of his 'reformed' state. That it is a close-up suggests that this is a dramatic turn to the camera, and whatever colour his eyes are at this moment show what fate lies in store for the character later down the line. In this particular instance, his eyes are blue much like his mother's, and just as they are in the Sacrifice trailer immediately prior to and after his failed assassination attempt on Valkorion.
To summarise, it seems from the images from the trailer that a dark Arcann keeps his 'edgy' cybernetic look in an attempt to keep his intimidating look, whilst a redeemed Arcann sheds the majority of his cybernetics in an apparent humbling attempt; with the amount of scars which 'earned' him that mask, he will actually look fragile and very much the shell of his former self.
Hypothetically speaking, if Arcann is redeemed, then there is a chance that he'll actually join the Alliance alongside his surviving mother (yay for more Senya!) and become a full-time Companion. I can't see many people being too happy with this, given that for the last sixteen Chapters he's been trying to kill us and many people have vented their frustrations at being unable to kill him at this point.
This outcome will also be very hard to explain to the rest of the galaxy. Arcann is renowned for being an absolute tyrant, and the Alliance was formed to depose him and end his threat forever, so I can't see many systems agreeing with Arcann's joining the Alliance.
Although it would be interesting if this had the chance to ruin an allegiance made at some point prior to his possible recruitment. Sort of like the choice between curing the Genophage and securing the Salarians' aid in ME3; you know which is the 'sensible' short-term choice, but you also want to give the other option due consideration for potential long-term gain.
A Dark Arcann (Darkann?) may also be permitted to join the Alliance as well, but I can only see this being a temporary thing. Either we spurn him or kill him to prevent his inevitable betrayal or he tries to leave of his own accord when 'his' part is done. If this is the only way Arcann can be killed in Eternal Throne, then people who tried their very best to engineer this outcome will be happy.
Although if the path to Arcann's fall isn't obvious and people accidentally redeem him when they weren't trying to, I can see some people being very miffed about that.
One final person to consider in all this is Arcann's father, Valkorion. Good ol' Valky has been engineering our path to the Eternal Throne, telling us constantly along the way that Arcann must be deposed and that he is our biggest threat to securing our destiny. If Arcann is not only redeemed but allowed to join the Alliance, Valkorion is not going to be happy. He likes his plans to be laid without upset, and his son surviving and aiding his new puppet could well be a significant blow.
This is mostly purely hypothetical, of course, but it's interesting to note just how much potential has stemmed from just three Screenshots. Since the trailer, BioWare have come out and all but confirmed that there is some truth to all this hypothesis.
It will be interesting to see how these moments play out. Whether or not they play out as hypothesised (although I implore anyone who is well-versed in data-mined story information not to confirm or deny anything in the comments) remains to be seen, but it's still going to be interesting.
All the same, I love the fact that we will most likely be influencing another character's alignment through our actions. It's been far too long since we had a 'Jaesa' type character in SWtOR, and Fallen Empire didn't really provide us with such a character-defining moment, which is strange given how much of a KotOR love letter it seems to be...