[Red Squirrel]

I would just go ahead and turn it into a GFCI in the bathroom. There is probably already a dedicated outlet in there anyway so who cares if that particular one is not 20 amps and not dedicated? If some inspector sees it and does not like it then it could just be replaced with a blank plate, but from a safety point of view there is zero issue.

If it's at eye level, you could also just hang a picture there.

 

[Red Squirrel]

Speaking of hidden junction boxes, I had a light in my basement go out the other day. A wire was loose. It was not hidden so I was able to fix it, but it just comes to show the importance of making them accessible.