TL; DR: Is it possible (and if so, desirable) to configure my OPNsense router to handle non-standard traffic instead of needing to configure each client device manually? Examples of what I mean by ‘non-standard traffic’ include Handshake, I2P, ZeroNet, and Tor.
If your looking to allow that kind of traffic in and out of opensense, then yes if you use it. Just be mindful of what you need and only allow that in, outbound is normally everything.