Yesterday, I stumbled upon a few SRL files that are stored in some romdumps. These are WMB programs, but yet contained encryption information which is only intended for card use. It is kind of odd they would left that in. (7 out of 52 SRL files)
I found an unconnected button input on the mainboard named "R03" close to the SL1 contacts. It is mapped to bit 3 of the I/O register which also contains X & Y buttons. The purpose is still unknown.
Since a while, Nintendo started using Matrix Memory ROM chips for their cards. These seem to require a bigger latency setting. This also gave thought to making a CompactFlash (or SD) converter. This way you can connect two media cards and copy stuff from one to another for example.
I also had an idea of connecting mainboard signals to an FPGA and USB port to turn it into a real developer's system. This will include video and both card/tridge slots. I will call it Dev-a-Station :)