I have settled with a 16×16 capacitor array module, which I routed (with great pain) with Eagle:

With such a module, the design is more flexible so I can implement as much RAM as I need or want. I can swap modules if one is found defective. I can build as many bitplanes as required, for example for the 17th bit for parity.

The above layout uses 6mm diameter capacitor, though I also have 5mm in stock, at least only one board model is manufactured.

For the driving circuits, the best I could come up is a 256-words array. Each bitplane needs their set of relays (I tried otherwise and failed, or else I'd need tons of diodes and stuff, which makes the system more complex and probably delicate).

Each bitplane then has 15 relays for the X MUX16 and 15 for the Y DeMUX16. Plus the grounding relay, that's 31 relays per bitplane. With 17 bitplanes, that's 527 relays for 256 words... and 2.7A @12V=32W for the static power consumption.

Pretty simple, right ?