They have tried variations of this since time immemorial (we can argue about "price reasonablé") but there's just not much you can do with it that you can't do much cheaper or simpler in other ways.

The Xserve has been dead for 15 years now, and it was never tremendously amazing (though it was nice kit).

Apple apparently has some sort of "in-house" xserve-like thing they don't sell; but turning that into a product would likely be more useful than a Mac Pro, unless they add NUMA or some other way of allowing an M5 to access racks and racks of DIMMs.