I guess one good thing is that you only need one hardware solution for all future projects as it's FPGA. You won't need to worry about future compatability issues as long as you have expandability in mind.
For these kind of projects I also think an open source GPL like solution is the best, so similar projects can flurish unhindered. This threads fight and legal, emotional and monetary issues also shows that using P96 is not the best solution.
Also, I don't think AOS 4 users are going to flee to M68k/Vampire as -- which should be very very obvious by now -- they want something different than M68k users. I bet a lot of them are going to buy an A600 and Vampire and probably enjoy it a lot, but abandoning AOS 4? Most probably not.
