I only have one small objection, and that is not being able to see the LINK and ACT LEDs as a diagnostic tool. It's not something I am hung up on.
As for Gold anything sticking out the side of your QL, well.... 70-something-% of the board area is free. The height of the (S)GC RAM is too high to stack it over another board. I'm laying this out as a functional prototype with a paste-able ethernet and memory block, so they can be quickly and easily moved and re-oriented. The original thought was to have the jack on aboard that fits in behind expansion cards and makes a new hole beside the ROM port, but unfortunately that would be out of spec because the jack contains integrated magnetics, and the distance requirement from the IC is quite strict. So for prototyping I will make it a large board, and for those that want a small board they can have it very easily once everything's confirmed working.
In either case, a nice matching ABS printed cover would be available for those looking to secure/protect their (S)GC. One idea is to use a short single ended ethernet cable to the socket, and the other end going to a CAT5 keystone molded into the case.https://www.monoprice.com/product?p_id=1039
Looking at it, the expansion could be as short as ~55mm including everything. That would add 43mm to the length of a thru-card.