There are a lot of things they COULD do. Hard to even debate such topics in a meaningful way because many things we thought Disney wouldn't or couldn't do...they ended up doing.
I don't think they could completely block trades into non-Home resorts unless they remove a resort from the
DVC program. In other words, DVC could not block all owners from accessing Aulani unless they remove Aulani entirely. And there's no practical reason to do that. Much of the appeal to DVC lay in owners' ability to book 11 or 12 different resorts rather than just one.
That said, I suspect there would be ways for DVC to alter the 11/7 month booking windows to the disadvantage of resale owners. The POS which governs DVC only guarantees us a one month Home resort booking advantage. Seems to me they could create a system in which Direct buyers have the 11/7 month booking rights while resale buyers have 11/5 booking windows.
Could they do it? I'm no legal expert but yes, I think they could.
Would they do it? Your guess is as good as mine.
IMO, it's more likely that we will see perks and another ancillary benefits limited to direct buyers. Someday we may find that only direct buyers have access to things like the Annual Pass discount or ability to purchase Tables in Wonderland card.
Strictly my opinion, though.