Don't understand all this FPGA code being wasted on custom boards that take years for the public to get!
Just My 2 cents forth!
And The Bonus is it's stand alone! No real Amiga Needed other than a Case 
everybody has their own bias. but here are practical reasons. developing a cpu accelerator first, instead of a complete system (as for example natami was, admittedly a custom construction, but there are people running minimig on altera de2 and the like), allowed to start with the basics and be able to prove the compatibility of the cpu core against the genuine chipset.
as you see, in result vampire accels are developed further and in a higher demand than other proposals.
but if you want, why not approach the team with a cooperation proposal. maybe they get interested and let you develop a support for your preferred platform.
