If you’re interested in porting gdbserver/GDB to other Haiku archs in the future, there is not much work needed. All you need is to copy/paste the right parts.
For gdbserver, the only architecture-specific code is for getting/setting CPU registers (look at arch_debugger.h for details on how to do that) and getting the size of a software breakpoint instruction (look at the kernel’s arch_user_debugger.h for the information).