Yes, as just an Amiga, it's not worth it.
I think if he were building it for Amiga fans, it wouldn't be feasible..
But the other markets (Have you seen the price for the Firebee ST FPGA?) are why, I think, he won't have any trouble.
I'm probably going to get one eventually, but I'm thinking about Amiga/ST/and my Arcade machine...
Mike has said that he expects his "biggest" audience to be the Arcade machine crowd..
p.s. Yes, maybe 10X the price, but how much would an Amiga 1200 with 40M of ChipRAM sell for? :-)