Oh well, since I was silly enough to talk about it, I may as well spit out some details, in general it is not so interesting if you have a M4 + XMEM already.
The prototype board in shape is designed to fit inside a GX4000 console, unplug the Z80 cpu and plug it into the "GalaXy" board (what does GX4000 mean anyway?). The board then plugs into the Z80 socket on the mainboard.
It's equipped with a USB port, with the intention to fit in a wireless mouse/keyboard transceiver, bringing the GX4000 to a fully usable CPC+ without soldering 100 wires in

Mainly because I wanted to have a compact cpc, that can be on my desk along the PC.
Some other things should become possible with this system (databus exchange) which was not possible via the expansion port.
It will also be possible to fit internally to a regular CPC, but less interesting of course. Some revisions will need a mirrored pcb layout (CPC+).
Anyway it may all fail, I may loose interest etc.