Haven't built one, but a couple of thoughts come to mind:

1. The LCD version of this (and maybe the solenoid/piezo?) seems to require destructive disassembly.  It's the owner's board, but M122's are desirable to buckling spring fans, and it would be a shame to gut a working one.  There are other ways to get or make a Cherry MX battleship.

2. The PCB could benefit from some relief cuts.  This is a lot of tension, and while using the thin 1mm as the designer says should help, a lot of the writeup seems to focus on managing that tension during soldering and assembly.

3. This is a LOT of hotswap soldering on pads to do by hand.  I would not enjoy the work, personally.  I think the whole thing would benefit from a reflow setup maybe?

4. Now all that said, this is really intriguing and I love the idea of solenoid keyboards.

There is no base standard when it comes to kitting, but the one I posted below is generally what the average kitting will look like (except for 1.5 function, that isn't common in base at least)

It really depends on the person, but generally a good set will accommodate all of this at the bare minimum (there are some exceptions, I have seen people remove 6.25u bottom row for smaller runs with sp for example)

For extension kits, you generally see stuff like mx hhkb support, r3 and r4 pg dn and up, shinethrough caps that sorta thing. But again that varies among designer, If I ever run a keyset mx hhkb support will probably be in base.

Thanks.  My issue is always finding wider keys from sculpted profiles outside their normal rows. Even as blanks, that's not easy, though it certainly looks like I might have some options with R3 1.75u and R2 1.5u.  I am noodling around with one more hand-wire project before I start exploring PCB design. I haven't quite figured out what it'll be, but accommodating sculpted keycaps is something I'd like to include.

A catboy themed hali project? Ugh, it's tempting...

Really cool board and concept, I just wish that there weren't all the seams in the top-case, though of course I understand that they are necessary for the concept to work!