This is a a feature/enhancement request.
"Whats the limitation or missing functionality you have encountered?"
Recently I was wanting to find out which pages (i.e Page: namespace pages) on Wikisource I'd changed to "Validated" status as I had concerns that some of them may be affected by parser migration issues, due to some highly specifc formatting I'd used or encountered.
Unfortunately it's not straightforward to do this because other than manually rechecking diffs (which could over a 10 year editing history run into the thousands) or a database dump, it's not necessarily possible at present to find when the page quality changed in an easy manner. The current page quality is currently stored in the "header" data for a given Page:
<noinclude><pagequality level="1" user="ShakespeareFan00" />...header content...</noinclude>
being an example entry which is located at the start of the wiki-text for a page..
"What is the desired functionality?"
- When the Page Quality information changes... create a log entry in an appropriate way, which can be used to generate an appropriate report/log on Special:Logs, namely a "Page quality" log...
- Create a new "filter" for Special: RecentChanges or Special:Contributions that can filter edits based on changes to the Page quality setting, when looking at Page: namespace pages, either based on the Page: content mentioned above or in respect of log entries.