One thing McVay has been quoted on a couple times is how they're all going to move around. But yeah at some point they're going to have to settle on a "top 3" who are their best look for a given defense on critical downs, starting the game, etc. I'd guess we'll see something like this:
X: Kupp. I think Kupp's best position is the slot and he's going to have a lot of snaps there I'm sure, but he'll end up playing a lot of X because he's big, has strong hands/physique and route running, it allows Woods and the others to be more effective. Woods will be here a lot too, and hopefully one of those two tall kid wideouts who will be fighting for their lives, but in the end Kupp's route running will play best out there even though it will affect his numbers going up against the best corner on a lot of snaps. That said, IF a guy like Thomas starts to put it together and splits time with Woods at X, that would be real good for Kupp.
Z: Tavon. I don't see Tavon as a good slot guy because he's not strong over the middle, his catch radius sucks, and when you need short yards he might drop it. Z's a great spot for your most explosive option, which Tavon is. He does have speed and at Z can be schemed into a free release and/or run go routes and posts and take the top off. So I think he'll do a lot of time here in this offense provided he works on his routes and sharpens things up.
Y: Woods. Again these guys are going to move around. But Woods will be a real dependable possession option for Goff out of the slot so will probably log the most snaps here even though it'll probably be close. I see Woods as on the field a lot for dependability, in the slot and out wide at X, maybe flip-flopping with Kupp a lot.
This discussion gets crazy when you start talking about non-11 personnel. Like who's the guy getting the lion's share of snaps in 13 personnel lol. Gonna be fun to attend camp this year, I'll tell you that!