Nice .. don't suppose you could make a schematic of it could you ? I've been trying to find one of those for aaagggeeesssss .. be quicker for me to make one! :-)
I'm not quite a power user but I do have :
2 * C128's
1 * C128D
1 * 1571
1 * 1581
2 * 1541-II
1 * 1541
1700 REU (512K)
MMC64
Mouse
Of course only a C128 is plumbed into it all.
Just need a port expanded like yours to make things easier (or make one! :-)