I hope we get some non PHB subclasses, especially hexblade. If nothing else, these will probably get modded in easily, as subclasses rarely require new assets.
I certainly hope that Wyll gets redone as a hexblade. Not only will it make more sense, he'll be a more useful companion character.
Not going to happen. His patron is a character in the game and part of his quest line.
Edit: that being said, Larian did see that they were looking into options to respec the companions, which doesn’t make any sense to me seeing as most of their stories are built around their class, so who knows.