Until I did a rewatch of VOY a couple years ago, I forgot that Icheb was even a character on the show. Clearly the person in question is an Iconian.
I am sure the trailer has more than just the first episode shown. IIRC Frakes only showed up for filming in front of the camera very late on in the season, suggesting he and Sirtis appear in the back half.
That is frequently not true. Probably not the first episode, but they could appear early on. The conversation Picard & Riker have indicates it's early in the process, after the admiral has thrown Picard out of SF HQ. They could have been working around Frakes' & Sirtis' busy schedules.
No doubt some of the first scenes shot were the ones that would need the most CGI work and post-production tinkering. I seriously doubt much work had to go into putting Picard and Riker in the kitchen and dock, so they probably waited to do their scenes til last.
Save for reshoots, TV series tend to shoot in order, even in modern serialized shows, because directors typically only direct 1-2 episode blocks, and need to spend time on post-production after the shooting is finished.
Even presuming they dyed some grayhair - and gave them a perm - it's more likely to be Icheb than Chakotay, because the exposed skin looks too pale for Robert Beltran.
I'd love to see Chakotay again and it would be a nice way to progress Seven's story. Hope it is him. I know he never loved the show and this would be an appropriate way to conclude his character.
I feel Beltran and his dissatisfaction with VOY is a bit of a chicken and the egg situation, in that I'm unsure how much TPTB didn't focus on Chakotay because he was a bad actor, and how much he decided not to bother trying because TPTB weren't focusing on him.
Well... That kind of wood does quite often drain the sap from its host. It also has been known to have a mind of its own.
Does assimilation + reverse assimilation increase or decrease your expected life span? Assimilation should fix every single congenital time bomb ticking away inside you, and Drones are "practically" immortal, so that has to help? (Did the Borg fix on Picard's Irumodic Syndrome get accidentally reversed by Bev?) Until a Federation Surgeon elbows deep in guts, starts hackslasing away, pulling out carburetors and crankshafts, making a bloody pile of machinery and mother boards beside their bio-bed.
Considering Voyager instituted the insanity that Borg don't reproduce, only assimilate, I'd hope they don't age. Otherwise their attrition would be something fierce, and they'd have to continually expand (or keep unassimilated planets in reserve) just to maintain numbers.