User-local moderation will be hamstrung by the lack of data. Sure, you can block certain users or reorder the results a little bit, but anything interesting would probably require the server shipping over huge amounts of data to a client which may never even do anything useful with it, which sites are unlikely to do.

Your best bet if you really want this feature is to implement it yourself server-side with just enough knobs to make it useful for your user-local case, and hope that other sites agree...