MC Breakout
The memory card and controlled slot share the same protocol which is a bit of a mix of SPI and I2C. Several third party devices and development projects started cropping up, using ESP32 or similar recent microcontrollers as interface with the main CPU.
The breakout board design files are committed into the repository, and are available through oskpark too.
It is designed to fit snugly inside the memory card port, being the same width as a normal memory card. Unlike a genuine memory card however, it won't have the vertical walls inside to guide it through properly. It may require a little bit of jiggling to insert properly, pressing upwards to make sure you're working against the flap spring. While it's going to be snug enough to not rotate in the slot, it may stoop a little as it won't have the full plastic shell to hold it straight.
If ordering PCBs, it is potentially relevant to require ENIG plating for better contact. If possible, one should request gold finger chamfering. A 2mm thick PCB should be preferred for the best contact, but may be prohibitively expensive, and a standard 1.6mm thick PCB can still do the trick.
The bottom side of the PCB is in fact technically facing up when inserted into the PlayStation.
Top side:
Bottom side:
The signification of each signal is better described in the esp sio development project. The signals are straight in the same order as the memory card connector itself.