A few things it might be good to think about having landed #10272:

• we disabled a few tests. We should fix and re-enable them.
  • sytest: Outbound federation will ignore a missing event with bad JSON for room version 6
    Re-enable room v6 sytest #10345
  • sytest: Backfilled events whose prev_events are in a different room do not allow cross-room back-pagination
    Reenable 'Backfilled events whose prev_events...' sytest #10292
  • sytest: Federation rejects inbound events where the prev_events cannot be found
    Unblacklist fixed tests #10357
  • complement: Outbound federation will ignore a missing event with bad JSON for room version 6
    Fix 'Outbound federation will ignore a missing event with bad JSON for room version 6' complement#152
• There's nothing stopping the queues building up almost indefinitely. We need to figure out what to do if a server can't keep up with the inbound traffic. Prune inbound federation queues if they get too long #10390
• We previously had a rudimentary form of this queue which kicked in while we were joining a room over federation (see room_queues in FederationHandler. I think we should update that code to use the same logic. (parking this for now - we'll revisit it as part of future join work)
• Handle any events left in the staging area after restart #10295
• The new queues need some monitoring.
• We now only process one event per room at a time. Not expected to be significant