Even if they just did a TKL, doesn't their existing membrane allow for them to just cut down in size? I thought that is what some people were doing when restoring SSKs.
No cutting and repairing the membrane (like hasu did with his 60% buckling spring) is very difficult and expensive. It is probably possible to roll up the membrane and fit it in the case, but you have to be careful still.
I'm pretty certain that the way to get more appeal for this is to make it new, not old. Everything on your list is expensive and a lot is unnecessary to most people. The majority of people who fund a kickstarter campaign, assuming they aren't geekhackers, will probably not be interested in multiple keycaps colors other than the ones they buy, and creating more will drive up the cost. N-key rollover has almost no practical applications besides being something to brag about technically, and would make development more expensive (why not use PS/2, anyways?).
Same with the DIP switches and detachable cables. More money, more people required.
If this were to be a thing, it'd have to have modern appeal. I would never have a BS on my desk because its bezel on a TKL makes it almost as large as a 104-key board, and it's just pointless to have all that. Lighter, weaker as a result (hardly an issue, it'll still be better than Cherries/Topres), but again built for popular appeal.
The reason I got my first cherry KB (WASD V1) was because the KRO of my current model M was not enough for several applications I used daily. Also: PS/2 is dead. There is almost no reason to use it nowadays.
keycap colours are already available from unicomp through their new process and will not affect the price in any way. If unicomp were interested, they might advertise that more. Last time I checked, DIP switches were pretty cheap and jumpers were already available in unicomp keyboards.
I'm not sure what you're getting at here. There are very real costs involved in bringing a new product to market, but many of said costs are not high in very real terms. They come out as the high cost of tooling / process change, but if you are designing a new process or new product, you can greatly ameliorate these costs as they can all happen at once.
If you already have a product, changing it is expensive, but if you are introducing a product, and you need to change you tooling, process, etc. then it's not so bad.
This is more true with manufacturing / big business than with crowdfunding, but with DIY, the process is mainly by hand and the added cost of change is almost equivalent to the raw price difference in your items. this is aprt of why DIY lends itself well to custom work.
