A new build:
- checkbox to toggle primaries
- restore primaries to presets
- note that presets are deduplicated, so you won’t get both blender-like|base and blender-like|punchy in the list, only the first one (and also not my favourite settings, if your preset also uses the blender-like primaries, or only one of my favourite settings #1 and my favourite settings #2, if they share the same custom primaries)
- the list is refreshed whenever you click apply (even if the active item is select a preset). So, if you add/modify/delete presets, you’ll have to do that (or exit to the lighttable and come back to the darkroom) to refresh the list. I did not find any callback I could use to detect updates to available presets.
- a new preset is available, unmodified base primaries.
The good news is that your previous edits won’t (erm, shouldn’t) be broken from now on (I’ve implemented parameter migration, and will keep that updated for future versions from now on). 
Includes all changes from master, up to and including commit f7da3ef4 (so version gf7da3ef4).
https://tech.kovacs-telekes.org/dt-agx/Darktable-5.1.0%2B1129~g70a3d9bb0c-x86_64.AppImage
@priort @MStraeten @Dave22152 , please update your builds.