The Macintosh Portable can address 9MB of RAM despite only having 24bit addressing. I don't think the 8MB "limit" was any sort of hard and fast limit on Macs. The 24-bit Amigas were limited to 8MB of Fast RAM, but that was because of a hardware limit in the Zorro II bus. Looking at the 32-bit Amigas, they have a ceiling at $80000000 (2GB). Anything past that can't be addressed by the OS.