Depends on D19502. Ref T13151. See PHI719. An install ended up with an object with 111,000+ comments on it because someone wrote a script to treat it like a logfile.
Although we seem to do mostly okay with this (locally, it only takes about 30s to index a similar object) we'll hit a wall somewhere (since we need to hold everything in memory), and it's hard to imagine a legitimate object with more than 1,000 comments. Just ignore comments past the first thousand.
(Conpherence threads may legitimately have more than 1,000 comments, but go through a different indexer.)