Unless I am missing something, which is possible, a potential issue I see is that a few people with a lot of posts and merit can band together to keep a pet project on top.
Certainly they will try, but it will be much more difficult than before, which is what is important.
I bumped oldest (not locked) thread I could find and it seems working.
We should see how this is working in a few days, when spambies realize that their weather forecast discussion won't bump threads any more.
Was it this one by any chance?

I saw it and thought, hmm, maybe there's a bug introduced somehow, because the OP didn't bump it.