If this https://www.tomshardware.com/u…4s-mysteriously-announced is correct - there is likely to be a CM4S module in the Slice-compatible CM1-3 form factor, but with the SoC from the CM4 on it...
If this becomes a product available to end users - will anyone try it in a Slice?
Yes I am happy to try it.
I have two, one in the case and one 'barebones'. I modified the case with a heatsink for CM3 to connect CPU to case via some copper when I upgraded.
Pictures here:CM3 heatsink
It runs quite warm especially with video, so a CM4 may well be more of a heat problem, apart from if it will work with Libreelec / Kodi.
Mine are used nearly every day for music streaming or for playing my FLAC based music collection. Occasional use for video.