Many of the pie menus work again but there are quite a few problems with icons.
Searching for all new icon identifiers is a bit annoying.
To make it easier for others I created this "Icon Updates" section in the release notes: https://wiki.blender.org/wiki/Reference/Release_Notes/2.80/Python_API#Icon_Updates
I hope to get some help from others, who are more involved in the icon updates, to fill in all the missing information.
TODO:
- fix broken icon identifiers
- maybe some other problems in code that is currently not reached