Midrange FL options with a view to RF (one day)

I'm selling my 16-35mm F4L IS and want to get something in the midrange FL, with a strong preference for top IQ, that I can leave on the 5DS R 90% of the time for at least a couple years. I also have a trip to Europe coming up in a few months (if the world can hang in there that long ), and want to bring only a single lens.

I'm no pro, so don't mind a little inconvenience and can risk not getting "the shot" for something that's more creative, absolute top IQ, and fun. Heavy is ok. I've rocked a Zeiss 50mm f2.0 Makro-Planar for months at a time as a single-lens solution and really was only occasionally held back by the MF (I had a focussing screen on the 1DS ii at the time, not an option with the 5DS R). I'm looking at the Sigma 24,35,or 50mm 1.4 Art (the FL is my burden to decide).

• Has anyone else gone down the path of adapting a single prime for 90% of use (for amateur landscape/family/travel/wider portrait uses)?
• I enjoy WA landscapes, but is stitching more than occasionally a pipe dream, or have others integrated this into their favourite prime FL workflow? (I get that stitching usually only works for static scenes.)
• Do 3rd party lenses with f2.8 or wider still activate the higher precision centre point AF sensor, like with Canon lenses? Will adapted third party fast EF lenses lose any AF advantages when adapted to RF?
• Do 3rd party lenses uniformly adapt to RF as well as Canon lenses? The EF-RF adapter isn't like a dumb extension tube and has electronics of course.

The other option is to go with the more sensible, but less interesting option of the 24-70mm f2.8L ii again. I had a poor copy the first time, but was very pleased with IQ (when it came through) and willing to give it a go and send back to Canon this time if needed.

• Clearly the lens is still excellent, even across 51MP, but if I want to move to RF in the next 3-5 years, would you count on an EF lens design from 2012 adapted to RF to be relevant in 5 years (2027, whoah)? Or for longer term, is the money better spent getting an RF-native version when I switch to an RF body for longer term peace of mind? (I know that quality now should indicate quality later, but the 24-70mm f2.8L mark 1 ain't holding up wonderfully )

Many thanks for any shared wisdom here.