I feel MS is too invested in GP to drop day 1 for their games.
And while there is more to GP than day 1 MS games, I feel that this is the feature that people keep propping up as the definitive reason GP is the superior gaming subscription model available.
And so, I feel losing it is a massive blow to GP and I feel it'll have a massive negative effect. Just how many ppl who have currently been conditioned to getting these games day 1 are now going to buy said game day 1? I just don't see it being a big enough crowd.
Best I see is that that higher (or highest) subs get day 1 releases, and other subs have to wait.