Thinking through #5603, and the two getDefaultSystemFeatures reminded me of this:

1. We have many global settings that should be per-store. thisSytem and extraPlatforms are good examples. This works best after Split Store class #5729 so that we don't pollute stores like HttpBinaryCacheStore with these new per-store options that don't make sense for them.

2. We have too much ad-hoc logic around build remotes that should be fixed up to use per-store settings instead, as we did before with system features in 4720853

   • We should probably make stores that can build a subclass of stores that just are read/written. Then we don't have to do silly things like say what "extraPlatforms" s3://... has.

3. Separate stores for evaluation, building and storing the result #5025 (comment) remains a very good idea. Then many of the remaining settings which aren't per-store would make sense as an additional config parameter to this now-freestanding (not Store method) function.

4. Finally, there may be global settings that are for the libstore layer at all, and they can be moved to another downstream library.