I finally got a set of test key switches to check which are compatible with my PolyKeyboard.

What's needed? Actually only a LED slit that is 8.5mm wide. This is usually not mentioned in any datasheet, so I decided it's best to try out!

The result table:

From that you can see that only a few Gateron switches and the Kailh Sabre & Cream switches work without modification.

Luckily you get much more choice when you cut away the little centerpiece in the LED slit. This can be done with either a sharp knife or a needle file. With that you can use all switches with a compatible stem (the cross) and all entries that say "needle file" for the 8.5mm slit. I added an exclamation mark in case you also have to trim away a bit plastic from the side (so in fact a bit smaller than 8.5mm).

If you are willing to modify your switches a bit more, you will get a much wider selection. For example, there are a couple of switches that have a slit, but at the bottom (base) there are only 4 holes for the LED pins. With a Dremel or similar you could easliy cut though the base (but it will be a lot of work... for each and every switch).

Of course this list is not complete, not at all. It's only what I was able to test. Let's hope that this list expands at some point!

I really like the low profile key switches from the second set of test switches and maybe I can use such switches for the lower 3 thumb switches (or even the whole bottom row?):

Unfortunately those have an incompatible pin layout, so I'm thinking about getting some Cherry MX low profile switches and just cut a slit into them...