If so, this could be an interesting alternative to RethinkDB's changefeeds, as RethinkDB doesn't support joins on the change stream.
Currently continuous views must read from a stream. However, in the very near future it will possible to write to streams from triggers, which would probably give you enough flexibility to model the behavior you want if you could conceptualize a table as a stream of changes.
Our next release (2.1) is due in about three weeks and includes automatic failover/high availability. Feeds on table joins (and other greatly expanded feed functionality) will be in 2.2, which should happen ~6-8 weeks after 2.1.
(Sorry to jump in with a shameless plug; what PipelineDB is doing is super-cool; I also met the founders a few times, and they're awesome, smart, and very driven people -- I'm really excited about what PipelineDB has to offer!)
> diff <(cat a.txt) <(cat b.txt)