If you ask me, it would be Really cool if we could play other then a elite or spartan, allow us to play as a odst, a marine, a jackel, or a grunt. I've always thought how fun would that be since halo 3 if we could play them for online matchmaking, forge, custom games and even mini games and ranked playlist designated to that character or faction. Maybe even have a specific game mode that let's you chose one of the characters as a class for multiplayer. Personally I can't think of anything better then dropping into he'll as a odst online. Be so sick
I think it's a cool and interesting idea, but like another has stated, I'm not sure if Infinite is the right place for it. Maybe in another spin off like they stated. Or if they did allow it, have it be in Firefight, where you drop in as whatever other unit type and try to take out the team that's holding it. I could see that working but then you run into a bunch of balancing and gameplay mechanics. They have to make each unit feel unique while you play them, their movements, sounds, etc.
Definitely not against the idea. When I first read it, I thought Left 4 Dead but I'm not sure it'd be a good fit in Infinite. I have the same feelings about a Halo Battle Royale. I think Halo is perfect for a BR. I've even brainstormed ideas on how it could work, but I don't think it'd be right in Infinite.