It is an extremely short flex cable, yes. It has a bit of a bend, so it can stretch a bit.
I am not competent in those things, but intuitively I agree, increasing complexity is probably not the right approach.
One idea I just got (if the enclosure is custom) is to invert the order of things. Imagine that the pads for the interposer are on the other side of the board from the MXM connector. Then from top to bottom you get:
- Interposer
- Framework MXM adapter board
- MXM GPU
- Cooling solution
- Expansion bay module shell
Then the interposer pads are always topmost and the z-height is unconstrained to accommodate the normal MXM connector plus cooler of any beefiness (and jankiness)