Anyone has any more suggestions, ideas, lore to post, feel free.
I think you can fairly easily headcanon a reason for any of the races to join in with the Stormcloaks by just leaning into their anti-empire nature. The Empire, especially as it is now, has made a mess of things across almost all of Tamriel, and is so infested with Thalmor Kikery that any hope of them actually throwing out the elves and going back to war is highly unlikely.
The Dunmer don't like anyone, but a lot of them especially don't like The Empire for all the fuckery they were putting Morrowind through during their occupation. When I play Dark Elves in Skyrim, despite the Grey Quarter shit, siding with Stormcloaks is almost a given for this reason alone.
Keep in mind, the tension between the Nords and the Dunmer isn't even primarily race motivated. The Nords feel slighted by The Dunmer because the dark elves want all the benefits of living within the city and being citizens of Skyrim, but throw their hands up and say it isn't their problem when it comes time to join in on the fight for Skyrim's independence. With some stretching I think you could very easily come up with a deal between the two groups. Hey, fight for us and we will elevate your people and put our differences aside, type shit.
Implying there will be any racism in 2020s Elder Scrolls.
God... They're going to nigger up all the races, aren't they? For some reason there will be black Nords and Imperials. There will no doubt even be nog Khajiits and Argonians, who will lecture you on how terrible it is to expect Khajiit to not be thieving skooma addicts because it is just their culture and socioeconomic factors bro.
Fuck it's going to suck.