Proposal: Proof assistants
I also wonder if these questions should be migrated to the new site if it's created successfully?
I believe searching by tags on StackOverflow already shows a looot:
The above tags are strictly about proof assistants, but mostly using them.
On SE CS, there are also plenty of them:
We also have questions about designing and implementing proof assistants.
On SE TCS (pretty much the same tags):
To add to your answer, there are quite a few on Math.SE:
Some of those tags are slightly abused / not specific to proof assistants, so one has to sift through them.