Next point release from the 2.4 branch.
Major milestone To be bundled with GHC 8.8; Nix-style local builds (aka V2 UI) becomes default; V1 (i.e. non-nix-style) CLI UI deprecated (and maybe even removed);
When nix-local-build becomes default, this bug is irrelevant. (e.g., sandbox and build/install tickets)
This issue must be fixed before new-build becomes default. (should maybe be merged with milestone:3.0)
These features will not happen unless someone steps up and implements them.