I just waited about 3 minutes for "emerge @x11-module-rebuild" to START the "Calculating dependencies" thingy. During that time, I had no visual feedback at all. The process seemed pretty much CPU-bound, and according to strace was reading stuff in /var/db/*/*/CONTENTS of such stuff as KDE and similar. Guess it tried to find files installed into a given directory. But having some kind of feedback during that process would be highly desirable.
We can add an asynchronous interface for set loading, and break that /var/db/pkg loop into a series of iterations that are scheduled on the global event loop.
Here's a minimal fix which defers package set loading until after the "Calculating dependencies" message has displayed:
Use the event loop to update the spinner:
This is fixed in 18.104.22.168 and 2.2.0_alpha167.