What’s the problem?
Basically the hw you run it on. You need memory that can fetch 64 bits every OCS cycle. You know, the actual basic difference between OCS and AGA.
The rest is implementing the logic that was in AGA. Compared to making the Minimig in the first place that is not a big job. And it has been done already as others here have said.
AFAIK the Minimig hw was not designed for anything but OCS and I am guessing that it can't give you enough memory bandwidth.
But your question seems to be more about the Vampire - that opens a whole different can of worms...
Note how all the other solution implements _everything_ in an Amiga. The Vampire has to work together with the innards of your 500/600/XXXX. I am still curious about how they will implement floppy drive access as that is physically wired to the native chips but somehow the data will need to end up in the Vampire memory.
