One of the first steps I'm taking in setting up x86_64 support for haiku is updating haiku_loader to support elf64 binaries. I felt like it would be a bit more logical to be able to boot a 64bit kernel before trying to build one.
There are a few hurdles to jump before haiku_loader is ready to load a 64bit haiku kernel. For example, we need to add the code to detect weather a kernel is an elf32 or elf64 binary. We need to load it accordingly and finally we'll need to modify how the kernel_args data structure is handled to support 64bit pointers.
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.
My project for the GSoC is to start the Haiku x86_64 port by completely porting the kernel and modifying the bootloader to load a x86_64 haiku kernel.