Are you talking about the C-40? Or the T-43?
The T-43 is going away with Randolph - the AF Nav studs will just train on the T-6 and T-1. The Air Force C-40's, AFAIK, are odds-and-ends planes for medium theater lift, like the Navy C-40A's.
It would make sense for P-8 pilots to train on the T-1, since that's what it was designed for - a light jet with big jet handling for training big jet pilots - but I'd be really surprised if it happened. There's no money for buying more jet trainers right now, we've already got the T-44C program going, and the AF is done sharing the T-1's they've got with the Navy.