Every PEX install I've seen has the one feature that makes it all worthwhile: a centralized cutoff manifold. Every faucet is able to be cut off individually from a single easily reached location using clearly marked handles. Like a breaker panel but for water.
That alone would make it...
Hold up-- here's the solution:
Using scrap 1x4 lumber cut a board out that is 4 inches longer than the diameter of the hole you need to cover. With a screwgun ready to go at hand, take the board and put it in the hole, behind the drywall so that the board overlaps existing wallboard on both...
I've done the obligatory search both here and elsewhere and think I'm ready to ask the question that I've had.
Now, removal of the existing tub doesn't appear to be a big deal and I'm not apprehensive about that. Disconnect everything, cover and smash. Easy and straightforward demolition...