I agree with cyriously about the costar stabs. I couldn't care less since cherry/gmk stabs aren't perfect stabilisation solutions anyway. It'd just suck if a v2.0 came out and we'd be stuck with costars.
Although it'd make life easier if we can just buy the set together with the main GB.
As far as the 3u. I have 2 pairs in white and black, concave, spacebars. They're pretty easy to get via aliexpress and/or KpRepublic (I think).
If anything, a small solution to salvage most of the case design would be to:
1.5, 1.5, 1.5, 2.25 (split) 2.75, 1.5, 1, 1, 1, 1, 1
This keeps row length, but has the "more abundant keys"
PCB stabs ain't perfect but is the best solution we have right now. I would argue that GMK screw-in stabs with the good mods are pretty close to perfection in this field (or Zeal v2 stabs). At least for the perfection we can achieve on stabs.
The fact that you can actually find 3u somewhere means really zero to me and many other people (no offense), if none of the common sets we have (gmk, sa) contains 3u x2, the whole keyboard is pointless. No way we are going to pair a random white or black 3u keycap with the sets we have, I mean if i spend $200 on a set of caps, the whole keyboard needs to be filled with these caps, not other random color caps in a random profile of a random material.
I think 3U spacebars are common in China (correct me if I'm wrong) hence ePBT offers 3u spacebar, even in base kits.
OP said 2.75 and 2.25 spacebars are rare, and I assume, here at least in GH, we mostly prefer 2.75 2.25 spacebars.
This keyboard is OP's vision, of course we can give feedback.
But if trying to cater to two different groups 3u vs (2.75 2.25) + cherry stabilizers requires too much rework, I'm fine with going 3u with Costar.
One solution I can see is to make two version keyboard. One is to cater GMK users (with customizable layout with non hotswap PCB), and one is the original in the first post.
IMO, personally, I won't skip this keyboard just because of costar and 3u spacebars. It's just too good.
I doubt 3u are popular in China, even if they are, i doubt 3u in China is more popular more than 2.75+2.25 (which are often contained in every "big set").
Even if it's true, he is doing this GB here for GH/Reddit/Keebtalk where 3u stabs are not even a remote option, so in that case he should do 2 plate style, one for China with costar and 3u x2 and one for the rest of the World with PCB mounted and 2.25+1.25+2.75.
Without mentioning how bad Costars actually are against a proper adjusted/modded pcb mounted stab.
IMO, even if i'm super excited for the design, personally I would skip this keyboard just because of costar and 3u spacebars, and i believe most of the people who can buy a $350-500 keyboard would do the same. It's an expensive keyboard due the design, i don't believe there are many people that are interested in buying this keeb if they have to use random 3u caps and costars.
Stabilizers can be ignored on a $60-80 keyboard, which is not the case.