Perhaps mundane, but little things like mechanical design matter. Those edge connectors were always a PIA and involved expensive gold plating on the PCB, and good alignment. Troubleshooting 101= reseat all the edge connectors. I was happy to change to ribbon cable for the busing and power distribution, but ribbon cables have their own ways to bite you. Especially if you use enough of them, for long enough.
Luckily most of my ribbon cable issues were caught early and managed. Some other console makers weren't so lucky, but they were probably purchasing ribbon cables and not rolling their own.
Shipping is always a special treat with big dog consoles... For some reason truckers always thought it was clever to cut the steel bands holding them to the pallets and stand them up on end, to save space in their trailer. We ended up building a crate around each console to discourage standing them up, and to support plenty of weight stacked on top. In my last large one we used a (relatively) light weight but strong and rigid frame structure that was similar to aircraft wings with two flat sheet metal plates (basically in tension) riveted to struts between them. This proved remarkably rigid for it's weight, but there were always a few customers who managed to trash them by dropping from some height on end.
FWIW it might be interesting for folks to see the inside. Most one off consoles I've seen involved entirely too much point to point wiring. I am more interested in unique routing architecture or features. One of the guys I knew who built his own console for his recording studio, put 7 band graphic EQs (with short slide pots) in every channel, which was great for how he worked. He did a lot of advertising work so he needed to dial in the EQ and start mixing quickly. Another unique feature (I designed the circuitry for, but was his idea) was a mute group facility that also operated as a solo in place, from the alternate "mute everything but the selected channels". In the mute master section we used 3 position switches for either off, mute entire group, or solo entire group. The group solo, command, would over-ride a group mute command, so you could combine groups for mute or solo and and get what you expected. He used that a lot to mix reggae tracks, and he was able to clean up percussive mixes that normally can get noisy and sloppy with multi-tracking and lots of channels.
Looking back I don't remember any guys who built DIY consoles (of which I know a few), who repeated that experience and built a second one. It was mostly a one and done experience, due to the personal time investment involved. Also with the commercial designs I am aware of, I don't know any(?) that were perfect the very first cut. I wouldn't mind revisiting some of my old designs, but thats life as an engineer. In fact when I worked in engineering management it was part of my job, to get the designers to release their babies, to the cruel reality of production, while I appreciate the desire to tweak things forever.
JR