As for characters, when Andor season 2 releases in April it would be great if we could get an Imperial Army trooper, that would be well utilized in squads using the "imperial trooper" tag, they were used a lot in the old legends content and the character model could be edited to make a mudtrooper (Mimban army trooper) from Solo, and perhaps Dedra Meero with some ISB-related unique ability that makes her more deady against rebels (which can make her a good counter to Phoenix squads) and that could also be used for if you bring in Agent Kallus from Rebels or Wulf Yularen.
Oh, and Jaina and Jacen Solo and Darth Caedus are a must for Legends fans, I'm sure doing that this year would bring lots of players. The event could also include light side Mara Jade and, if you wanted, Yuuzhan Vong invaders and their biological ships for fleet battles.
As for debuffs, I am not familiar with every debuff, so, apologies if this is already a thing but a "force drain" debuff to siphon health could be interesting. The "Corrupted Battle Meditation" used by Dark Side Bastilla Shan should be renamed "Battle Meld" and also given to Caedus, and maybe reworked a little bit?
In the event that the KOTOR remake comes out, KOTOR-era sith empire and republic troopers would make good additions especially since Revan's ability is for Sith Empire or Old Republic tag and there isn't too much variety. (And maybe if you wanted to do another thing to promote the old republic MMO you could add Satele Shan and a TOR-era republic commando to match Malgus and his TOR-era sith trooper already in the game)
One last thing, it feels kind of weird for Merrin to be on the dark side. I get that it's because of nightsister magick and the nightsister tag but it still feels wrong. Maybe updating her to light with a Light Side Asajj Ventress and a nerf of the OP night mothers would be useful.