Unless you plan to do this as a hobby only or perhaps as a hobby business I don't think it's a very good idea. It'll never become a serious contender outside the Amiga geek world unless it offers something unique, something better than the rest. Efficiency only sells to engineers, it means nothing to anyone else.
The Amiga was good because it was fast, The Mac did everything in software whereas the Amiga did a lot of stuff in hardware so not only graphics and sound were faster so was everything else because the CPU was freed up.
These days everone uses the same approach, CPUs are now so fast you don't need to use hardware and the only area it's needed is for 3D and thats done very nicely by ATI, Nvidia and Sony.
Want to build a new "Classic Amiga", firstly dump the idea of using a 68K or compatible, even a low end PowerPC with JIT will outgun them. For the hardware use a FPGA, they're fast and cheap these days, anything else will cost you *vast* sums of money. For other graphics (3D) use an embedded graphics chip, ATI do them and there'll be supplies for a long time, they'll also kick the Kyro's ass.
The best addition you could include is a PCI connector - so you can plug it into a PC - and in doing so increase you potential market from hundreds of units to millions of units.
Oh and yes, speaking to Jeri is probably a good idea - she already has parts which could go into an Amiga emulator...
