FPGA and emulation is the ONLY way forward for Amiga OS, well OS3 anyway. All the Amiga software is 68k but 68k CPU's are dead and no longer developed. Once these new FPGA accelerators come out and hit the scene, that problem is eliminated.
As for OS4, who knows? PPC is a dying breed too and soon to be extinct, perhaps its only chance will be FPGA also.