This is a longer-term project, but as Codex develops, we should migrate the ProofreadPage extension away from OOUI and towards a Vue.js-based UI. This will enable richer UI experience and also (hopefully) simplify the UI.
There may be cross-over with the OCR tool and Wikisource extension: does it make sense to have some kind of shared Wikisource Vue component library?
Note that there's not a huge amount we can do right now, since Codex has limited widgets available so far.