since last year there is a positive trend in custom kits: there are kits that offer more than the base set. they have extended options to at least the following:
1. modular and solderable pcbs;
2. fully-compatible plates for the pcbs (with different materials and cutouts);
3. pre-cut foams for use between plate and pcb, and between pcb and bottom case.
this is a good thing. my observations with kbd67 variants showed that with recent structural improvements on the modular counterparts, both modular and solderable options now have identical typing feels and sound, compared to options that we had few years ago. (this might be due to keyboard constructions adopted in these kits also)
with these kits, the typical custom building process can be streamlined as follows:
1. start with a base kit with modular pcb, plus whatever extended options that you want. use it to test combinations that you wish to have, and tune them if necessary (without soldering and desoldering processes, this is relatively time saving, and you don't need to worry about potential pcb issues caused by soldering and desoldering);
2. get solderable pcbs and plates to make the combinations permanent (basically i just migrate everything from modular pcb to solderable pcb).
technically, you just need a case, and a set of key cap set that covers most keyboard layouts (both are essentially why budget for a build is bloated, besides switches), and replace only barebone builds when you want to. i really hope there will be more kits with similar choices in near future, and they can cover more options, e.g. form factors, plate types, etc.
If I ever go down that route, I will probably go down the 75% + cospad route. The 75% I can carry around with me, the cospad I'll leave in the office.
But so far I haven't seen any hotswap 75% PCBs. I guess I could put in hot swap sockets myself, but that is a lot of work to put them in and remove later when you want to make it permanent.