Answering my own question maybe, but I’m still interested in your thoughts about filtered replication.
Instead of letting my app decide which local docs to push, the app could push all of them (leaving ReplicatorConfiguration.DocumentIDs = null).
Instead I would make the Sync Function responsible for deciding which to accept, and which to reject.
How about scalability in this alternative design ? Would the push replication resend all previously rejected docs on every subsequent push ?