The max memory isn't an indication of that, the M1's max of 64gb is limited by LPDDR5 module capacities.
What would block a new Mac Pro would instead be DDR4 or DDR5 support instead of LPDDR5, and also PCI-E lanes. Both of which would likely require yet another change in silicon design.
What would block a new Mac Pro would instead be DDR4 or DDR5 support instead of LPDDR5, and also PCI-E lanes. Both of which would likely require yet another change in silicon design.