let me add my status update:
with the help of my trusting betatester
inian we've got CID and CSD read from a bricked 3DS using the original 4 wire HW mod via a raspberry pi SD slot.
for anyone interested the CSD is 00900F00320F5903B9FFFF87FF964050 which, as long as i haven't miscalculated, says that there is no global write protect set. (wont post the CID, unique traceable number n stuff)
oh and btw: the init sequence is different for MMC, at least in SD mode.
the SD mode (not SPIO mode) sequence is:
notation CMD[cmdindex]([argument])
CMD0(0x0) -> CMD1(0x40FF8080) repeat untill reply has bit 31 set (aka. reply & (1 << 31) == 1) ->
-> CMD2(0) reply is CID -> CMD3([RCA]<<16) (i used 0xBEEF as RCA, old habits) ->
-> (if CSD wanted: CMD9([RCA]<<16) reply CSD) -> CMD7([RCA]<<16)
which leaves the card in transfer state waiting to receive CMD42.