Reduce bandwidth used by polling
Polling for connections to contacts via Tor uses a significant amount of bandwidth. We could save bandwidth by polling unreachable contacts less often, or by polling less often (perhaps not at all) if we're confident that contacts can connect to us when they come online (ie if our hidden service is reachable).
For short-range transports, polling contacts in a batch may use less battery than polling them at contact-specific intervals. It may be possible to meet the needs of Tor and short-range transports by polling in batches, but not including unreachable contacts in every batch.