This is an enhancement request or even possibly an extension request. The latter of which, I intend to write myself, but I don't mind keeping some records on the matter and more importantly a discussion.
The idea of this proposal is to create the ability to watch a specific user's edits for a period of time (after which it will have to be manually renewed (such a time limit will be restricted to a maximum of 2 weeks per default, but will be configurable in LocalSettings). In addition, to further avoid Wikihounding, the right to use this feature will also be limited to sysops per default.
The idea is that often times a new user (or old user for that matter) may make a suspicious edit or two. Nothing that would either necessary require a warning, but might be suspicious behaviour to the sysop who discovers the edit him/herself.
Rather than keeping several tabs running of Special:Contributions open, it should be possible to watch a specific user like watching a specific page. The time limit is inserted to ensure an autocleaning list (where no longer interesting users gets cleaned off) and to avoid overreach of the functionality for potential harassment.
The edits by these users will appear in the Watchlist and in bold in the Recent Changes. Similar to how regularly watched pages do.