Nope he has to be registered to play for either a club in England (association trained) or us (club trained) for a full 3 years prior to the season start after his 21st birthday to be classed as homegrown one way or another. So basically he would have to play here for the next 3 years or play for another club in the premier league.
Given that he has begun pushing for a move away from Ajax I don't think he has any interest at all in staying another year anyway, so we can almost certainly rule out the championship as well. If we're moving for him now I think that makes perfect sense because Vinny will be totally gone this time next year and in all likelihood will miss X amount of the season through injury even if he has a great last year.
Pep has shown with Sane last year and Bernardo this year that he is very adept at signing players and bringing them in slowly, and I think that is probably the plan with De Ligt. I still think he would be mad to come here and fight two of the other most promising cbs in the world for a starting spot just to work under a coach who currently only has 12 months left on his deal, but that is up to him, and with any luck the boss he has given him a bell and said he plans on staying longer.