Note that the size of the virtual address space on current x86-64 processors is only 256 TB! (And half of that is usually reserved for the kernel.)
And inevitably, some programs take advantage of the other 16 bits to store data, so even if you get new hardware to use the full 64 bits and kernel support to match, you'll have to watch out for JavaScript engines and other programs randomly failing :)
And inevitably, some programs take advantage of the other 16 bits to store data, so even if you get new hardware to use the full 64 bits and kernel support to match, you'll have to watch out for JavaScript engines and other programs randomly failing :)