Currently Haiku is stuck in the 32bit world. This is fine for the initial BeOS R5 compatible release, but this is extremely limiting for future releases. It's a reasonable goal for Haiku to have a mature 64bit x86 port by the time the R2 release comes out. However ports don't become mature overnight. If full time work is put into porting haiku to the x86_64 platform this summer it'll be feasible to finish the port in a reasonable time to have it throughly tested and ready for the R2 release.
This is a companion discussion topic for the original entry at https://www.haiku-os.org/blog/nmentley/2010-04-28_gsoc_x86_64_port/