I'm working with some very large files and I run out of memory during the commit.

fatal: Out of memory? mmap failed: Cannot allocate memory

I'm hoping that a 64bit build will eliminate this problem. Are there any plans for this?

I think you may need to just build git for yourself for the time being :) 64 bit builds are larger, and it seems there is very little need for them as very few people commit larger than 2 gig files.