Full changelog can be found here.
I usually do a eopkg info python-qtpy to see the reverse dependencies to have a clue, but this won't cover everything.
Ideally you should grep the repositories to find were it is used but for that you should have cloned all the repositories.
I’m not entirely sure about this, but Spyder (Python2 version) might be the only package relying up on the python 2 support of this package. This package was included in 2017 to the repo in order to satisfy Spyder based on Python 2. I’d vote for dropping Spyder and flicking off python 2 support in this if we can...