Hello!
I feel like factions are a needed point to make the game fun. Make it where each faction has a story and a feel that is personal to itself, a story that being on one side will give you an amazing insight that the other faction doesn't have. It's a great feel to be in a position where the world is not one single storyline, but separated into stories you can find distinct enough and compelling and also gives you a reason to try out the other side too.
That being said, in terms of people playing with other people, I find no reason why, if you really want to play with your friend, you can't join them even if you're the opposite faction. Maybe not quests and story since that is personal to your faction (so not like ESO), but maybe any overworld challenges and instance content (FF Fates or WoW World Quests; Dungeon runs for the gear/loot and not just a story playthrough). There is in my oppinion no reason to stop people from playing with their friends (maybe you just don't like the faction, aesthetic or can't see yourself playing that side), but it as well shouldn't be something made as trivial as to make factions irrelevant.
I feel like there's a strong distinction to be made between immersion and accessibility, where your immersion is upheld through the faction you play, their story, quests, mounts, gear looks etc; and accessibility is the point where we can be like 'Ok, I understand that in the story and in the world I immerse in there is this divide, but that shouldn't stop me from doing non-immersive stuff with people that, otherwise, doesn't make sense to do if immersed'.
That's a bit vague worded, so I'll explain a bit more what I mean.
Immersion is upheld when you feel like what you do is in line with the feel of what you play: questing in your faction's levelling areas, fighting the opposite faction in contested zones, building your player house (that was mentioned at least in one of the dev videos) in the style befitting your faction etc. This all is part of what you do to feel like the character you play is in tune with their faction and your preferrences.
Then there's non-immersive gameplay, like running the same challenge dungeon for 10 times to get the achievement; going around the world to farm the same place for 5 hours to grind some gold; wiping on the same dungeon/raid/challenge for a few hours a night to down the boss. All these are almost not at all reliant on you feeling part of X faction and with their own feel to having overcome it (like most MMOs don't claim one faction or another canonically defeated a raid or a dungeon). This should be the point where it doesn't matter if you're Order or Domination, you're playing with people to overcome a game challenge rather than a faction-specific game aspect.
That's at least what I'd interpret would be the ideal compromise.