This is an interesting rumor but I can’t help but wonder why Apple would put an M1 Pro Max into its niche desktop when Pro users have been clamoring about wanting a modular Mac Pro, and given the event is likely to herald the arrival of the “consumer” M2 and a new Air.
Still, if it happens it might be a good option if I ever want to go back to the “mini life” and take my MacBook off my desktop (which I really don’t think is going to happen soon unless I develop a pressing need for a dedicated machine).