“Which, looked at in that way, is pretty optimistic after all. Why would OS X necessarily last two human generations?”
Exactly. My point was that 16 TB of memory per process represents considerably more room for expansion than we’ve had in previous memory addressing jumps. Many other things are more likely to be an issue than this limitation.
Like a motherboard that can take 16 TB of memory? Right now we're up to 4 GB chips, 16 slots on servers, 8 for high-end desktops. That's only 64/32 GB. Slots aren't likely to proliferate much more (except on very large servers) simply due to room on the board, so we're waiting for 1 TB memory chips, 2 TB chips for desktops. That'll be a while.
I know, virtual memory technically makes this possible today, but that much address space is usually reserved for high-performance applications, and it would be counter-productive to do that in virtual memory.