Idea: hybrid SX-1 + RPI 4

Here is the gathering which actually works:

For your curiousity, cartridges connected:

1-0: 4Mb memory mapper (8bits4ever PCB, soldered by @Omega)
1-1: natural FlashROM with real SCC chip (recently i started using for hosting the standalone latest alpha of Nextor to speed up file copy operations on MMC/SD on it, besides regular use as an SCC sound source)
1-2: empty (can't find what to add, everything i tried makes system unstable)
1-3: GR8NET
2-0: MMC/SD v.4 by Sharksym
2-1: GFX-NINE
2-2: SFG clone
2-3: another 8bits4ever expander with cartridges which use I/O only:
x-0: FM-PAQ
x-1: DalSoRi r2
x-2: MIDI-PAC v2
x-3: Darky

The setup is stable only on Sanyo Wavy PHC-70FD though. While trying to make it, had to try different arrangements, as some cartridges didn't want to sit in the same expander with some other one, or didn't want to work well in one or other expander, btw

(i didn't try RS-232 interface yet, maybe it would fit the free slot 1-2 ? hehe)