I've noticed that many of the newer BTC keyboards use these rectangular sliders on the stabilized keys, likely to simplify the chassis construction and cut manufacturing costs.
I've only ever seen these sliders on BTC keyboards. The earliest example is from 1999, whereas the newest example is as new as 2005.
I wasn't entirely sure that these were from BTC until I opened up the keyboard, where I found BTC printed on both the top and bottom casing. The example also had a very BTC-like FCC ID, starting with E5X. One of them even has the iconic 1.25u Esc key that BTC is fairly well-known for.
I also found these blue sliders in a much older BTC eKB-5190, which appear to be significantly longer than the newer black sliders:
As for the keycap mount, it looks as if it might support Alps keycaps, but unfortunately it won't. It's a different size altogether, and the slider is rotated 90 degrees, so even if it did support Alps caps, you'd have quite a hard time typing on sideways keycaps. Unless that's your kind of thing, of course.
Overall, this is something quite new to me. Are there any examples of these switches being used in an entire keyboard? Is BTC the only manufacturer that is known to use these switches?