I'd take a modernised A1200-compatible, kind of like the BoXeR was to be. I've no interest in "new" "Amiga" machines; retro is where Amiga is at for me.
- full 68060, fastest available, possibly factory overclocked
- "AGA+" chipset reimplemented (in FPGA I guess): fully AGA compatible; "chunky" graphics modes added; extend chipram size (or change to unified memory architecture?); VGA compatible output; S-Video output
- SDRAM (or DDR?)
- PCI slots; AGP slot ?
- USB ports
- USB keyboard / mouse / joypad inputs translated to old-style Amiga mode (ie: no drivers or other software required)
- IDE (or SATA?)
- PC floppy drive support
That would do for starters
Of course, I have no idea how hard or expensive any of it would be
Slight aside: how hard would it be to make a 68k compatible processor in a FPGA? What would the performance be ? Just curious