If you visit a topic in a category you have no permissions for
AND you are a logged on user
AND can gain permission by requesting membership, we should display a helpful message saying:
Hey, you can not see this topic, but if you join the AWESOME group you will be able to see it, [request membership]
just pick the first group if there is a multi match
This does leak out a bit of information about “who can see” a topic which we do not leak out now. However to leak this data you got to create a group that accepts membership requests, so you kind of opted for it.
I really like this feature request, going to slot it for 2.3