Thought a lot about whether 64k per page table block is really enough space, extensively considered going to 9bit bytes and 18bit alu/registers. Eventually decided against it after a lot of consideration, as I think it would make interop with other systems, testing, and other aspects much harder. Will stick with 64k per PTB for now, and can work around it later if need be by giving processes multiple pages using code overlays or something like that.