I would like to run
# emerge @preserved-rebuild --usepkg-exclude=@preserved-rebuild -vbka
during system updates, but sets are now not supported in exclude options.
I run 'emerge --depclean --with-bdeps=n -qa' after every update, so i have no build deps installed, rebuilding them every time is pointless. Also supporting sets in other *exclude* and *ignore* options could be useful.
The set expansion should be delayed until depgraph.select_files() is called, so that the spinner is responsive during set expansion, taking advantage of this code from bug #461412: