This idea isn't impossible and has already been discussed in the original MiniMig thread but it is much harder to do than the MiniMig v1.x
There were lots of reasons but look at the efforts of people to make new PPC accelerators for the A1200/A4000 that have come to nothing.
Having put that minor downer on the idea I do think it will happen eventually but your idea of making MiniMig into an AGA capable machine is quite an endeavour in itself as it requires redesigning the MiniMig to use a differet cpu and 32bit data and address buses etc, as well as probably changing to a different type of ram... oh and that minor matter or rewriting the OCS chipset to be AGA capable.
Like I say, good idea, think it'll happen but its gonna take time. Dennis is an electrical engineer, most of us that are coming up with these ideas are from other fields of expertise! So its taking a little while to learn any of thise stuff.
@AndrewBell
Piru's opinions are his own, but you'd be better off listening to him since he knows more about the Amiga and developing software for it than almost anyone on these boards. His sometimes rather negative seeming attitude isn't really that, he'd probably love it if you turned around with the aforementioned PPC MiniMig design totally open sourced and with a working demo board, but he's quite familiar with how difficult these things are.
Its rather like someone whos just discovered a computer programming language like basic and writtent heir first hello world program turning around and saying: "right, so how do I make Doom3"
Andy