Problem/Motivation
If we want to do #3079738: Add Claro administration theme to core, then we need to figure out how to actually add a theme to core as experimental. (This will be the first time we've tried!)
Both profiles and modules have a status indicator that they are experimental (profiles in the name; modules in the grouping):
Experimental profiles don't seem to get any special treatment when selecting them; however, when you select an experimental module it warns you for good measure:
And are included in the status report overview page, so we'll need a similar entry there for themes (and/or consolidate it all into "experimental stuff"):
Proposed resolution
TBD. Need to come up with a design similar to the above.
Alternately, something suggested by @effulgentsia is we could potentially fix #474684: Allow themes to declare dependencies on modules and leverage a required module to do the experimental warning.
Remaining tasks
TBD.
User interface changes
Yes; we'll need to clearly outlay a theme as being experimental.
API changes
Possibly.
Data model changes
Probably not.
Release notes snippet
N/A; there will be a follow-up issue to implement whatever we decide here, and that will probably need a release notes snippet.