You know, it would be really nice to just clean-room reimplement the whole damn thing and sidestep this entire disgraceful corporate toddler fight. Maybe I'm just talking crazy talk, but it doesn't seem like it'd be that hard; the documentation in the ROM Kernel Reference Manual, coupled with the fact that the whole OS is based around application reuse of what other OSes would consider to be OS-internal structures and code, gives a remarkably clear window into how the system works without even needing to get into disassemblies of Kickstart binaries.
(P.S. I know someone's going to mention AROS, but no. Whatever its other merits, it has exactly one 68k port, which is deprecated and not even for the Amiga, and one PPC port, which seems to require an existing Linux install. It might be an Amiga-inspired or Amiga-based operating system, but it's not an Amiga operating system.)