You have the bumplock, which blocks threads from being bumped so they sink to the bottom and disappear. But could you add a new feature that keeps threads from disappearing even when they have reached the bottom of the catalog?
It often takes less than 2 days for a thread to go from the top to the bottom and then disappear. And sometimes I go to sleep and 8-9 hours later I check the catalog and a thread I wanted to read is gone. It wasn't even near the bottom of the catalog but 8 hours later it's gone. It's annoying.
A 'life jacket' would keep threads from disappearing for a week or two. Many would end up floating at the bottom of the catalog but they could be bumped with news posts.
Candidates for the life jackets would be threads in which we dig for information or a worth reading debate or things like that. For example I remember an interesting thread about economics and it took me a few days to read it all and I had to bump it a few times just to keep it from disappearing.