Mine are 1) Xmodmap support/migration 2) breaking imagemagick's import (screenshotting) making my shortcut for OCR'ing text on the screen break.
It seems Wayland isn't going to be the default in Ubuntu 20.04 LTS, but if it wasn't for the risk of Wayland I would be on the non-LTS releases. At least Guix exists now so staying on LTS (released every 2 years) isn't that bothersome in terms of easily avoiding out-of-date software.
I don't have the exact command at hand, but it just uses tesseract. Something like "import - | tesseract <whatever options for language and page format> | xclip". The accuracy is not amazing by any means.
As long as it implements X, I don't mind, but my understanding is that the change is a breaking one.