Not too sure what alps switchtops you checked, but the openings on some SKCM oranges I have are about 5.4mm for the smaller dimension of the opening, which is about 0.1mm less than the stems on SA caps which I measured at about 5.5mm, and 0.2mm smaller than some cherry double shots I had around where the stems measure about 5.6mm wide.
Yeah, it was a quick eyeing. I noticed that the clearance might be too wide vertically, but I didn't want to keep editing my posts and seem like a know-it-all or make the message convoluted.
Yeah, the stems are a hair too wide on OG Cherry doubleshots for vertical clearance. I get a 5.62mm measurment on the stem with my calipers, indeed.
Alps vertical clearance is 5.54mm. Used an SKCL top housing, but they're obviously all the same in that regard, at least with Alps SKCL/SKCM.
I managed to get the stem through a housing with a bit of force, but obviously, this kills the proposition. You'd either have to shave the stems on the caps or the housing opening, which would then just become even more of a dust hazard.
I guess the best solution would be modified top housings AND modified stems withe a Cherry MX mount that still used the same internal dimensions of the original Alps sliders on the bottom end so it wouldn't alter the feel of the stem acting on the tactile or clicky leaves, but then that'd already be too complicated. I don't think anyone makes housings with slits anymore, so it'd probably already be quite an investment. If we use housings without the slits, then that'd alter the feel of almost every popular switch. The only switch it wouldn't effect that people like are bamboo SKCM Green. Some like bamboo SKCM Black, but still.
All to use your favorite Cherry caps. Eh.