Matthey, you are aware that most Amiga users are running some version of UAE and are perfectly happy with that?
I don't know about most but many are happy with UAE. I have UAE+AmiKit installed here on my used PC (<$100 U.S. but more powerful than any AmigaOS 4 hardware) and it is nice for some things but I still prefer my real Amiga which is not held hostage by a foreign OS (even with SMB networking setup between the Amiga and PC). I believe there would be a draw to hardware that is cheap and convenient (many people with a fast PC still use slower smart phones, tablets and netbooks) and enhancements to the Amiga custom chips and CPU would become difficult for UAE to emulate (MMU emulation already can't be used with UAE JIT for example).
I don't know if the specification has been changed now, due to the cooperation, but one year ago, the Minimig Plus was planned to equal an Amiga with 68030 CPU at 30 MHz. Furthermore it was intended to have space enough for an AGA core.
The DragonBall CPU was mentioned but it is only a faster 68000. There are several problems with that...
1) Much AGA software assumes at least a 68020 CPU (AGA was never released with a 68000 CPU)
2) Much non-AGA software assumes at least a 68020 CPU
3) AmigaOS 3.1 was the last to support the 68000
4) Finding 68000 only versions of programs is a pain
5) The 68000 is old and much less efficient for complex programs and/or programs >64kB (huge size at the time of processors advancing from 8 to 16 bit)
I don't expect compatibility can be good with the DragonBall past the late '80s and ECS. The TG68 CPU in a large but older Cyclone III (like Majsta targets with his new accelerators) with CPU+chipset beats it and this is not expensive. It may even be cheaper to produce the board without the DragonBall although it could be used for I/O and menu operation (the DragonBalls may already be purchased).