Problem: It can be difficult to get a quick insight to who an editor is and access the information relevant to them.
Proposed solution: Expand Page previews with functionality to show a small profile of a User. It could show join date, user groups, edit count over last 30 days, if they are blocked or not, a link to their talk page and contributions, and maybe something like their mentor from Growth. All kinds of little helpful nuggets of information. There could also be an optional lede/intro and page image provided by the user.
Who would benefit: Makes it easier for editors to get some insight into a user really quickly, straight from talk/history/RC pages etc. Makes this functionality, which is already a feature of the 18 year old navigation popups and makes it available to all Wikimedia editors.