Other than the semi-obvious "cross-platform support" - which I'm working on. It may be slower on 32-bit OSes, but I think I can make at the very least indexed tables work without mmap. And, apparently, Windows has something close to mmap (see below, my 64-bit rant thread).
I'm planning on multihash support, which will probably leverage multi-GPU stuff as well.
I've also got some ideas for smaller table formats that keep roughly the same performance - I think I can cut the table size in half for a lot of tables.
Any other feature requests for the cracker?