Going from an M4 Ultra (assuming it's 2 M4 Maxes connected) to an M4 Extreme is probably not easy - from the Pro to the Ultra you have only one chip-to-chip connection, but to an M4 Extreme you'd need a redesign of the M4 Max (the same way it'd need a different approach to M2 Max back when an M2 Extreme was first considered) with at least two interconnects.<p>Apple could also go the AMD way and have a central die with shared elements (caches, memory controllers, PCIe channels, etc) and multiple smaller processor dies. This way building an M4 Extreme or an M4 Ludicrous would be relatively simple.