Jalin Marshall will simply not be the deep threat, that would be a waste of his skillset.
Corey will be in charge of running off safeties. He won't be as successful as actually getting behind them, but as long as he opens up the middle-intermediate part of the field Dontre and Jalin can excel at crossing routes.
Noah Brown will absolutely replace Spencer as the "blocking Z" and Vannett will be the hybrid Y.
I don't see Curtis Samuel making a complete transition to H, that would be a waste of his vision between the tackles. Even last spring Urban said that Samuel wouldn't be moved because he plays tailback more naturally. Instead I think they're working Samuel at the slot so they can use him like a pass catching tailback - ala Carlos Hyde at the end of his career.
So, Thomas at X, Smith/Brown at Z, Vannett/Brown at Y, Jalin/Dontre at H, Zeke/Samuel at T
Zeke, Thomas, Jalin, and Vannett will see the most snaps in that order. Y and Z are interchangeable and set the priority as blocking or field stretch, H and Y can also be interchangeable when creating a pro(ish) singleback look for zone blocking schemes.
The Urban philosophy: recruit the best athletes, make the scheme simple, teach every player to be multi-positional.