Ok I'm going to do the following. I hope it is okay:

1) One subscription for the main feed, which is usually several hundred notes long. Every time a new note comes in, but no more often than some minimum time, I will rewrite it adding the new IDs, and including a since=now so as not to replay everything again.

2) One subscription for alternative feeds such as viewing a person's post history, viewing a particular thread, or viewing your inbox. This will be rewritten as the notes flow in for that feed just like for the main feed, but the filter will not have any "since=now" limitation, practically guaranteeing many repeats. This subscription will be unsubscribed as soon as they browse back out of that alternative feed.

Both subscriptions will be limited to reaction/zap/delete event kinds.