Hello tor-dev,
Steve Engler (currently part of the Shadow team) and I have a paper of possible interest to appear at ARES 2021 next month.
It's a design of a multi-threaded relay architecture, of possible particular interest when considering relay support in arti, for example (though the proof-of-concept implementation is based on the usual C codebase).
If you're interested, here are previews of:
Paper: https://cs.uwaterloo.ca/~iang/pubs/mttor-ares21.pdf Video: https://www.youtube.com/watch?v=41a6nLUJye8 Code: https://git-crysp.uwaterloo.ca/sengler/tor-parallel-relay-conn https://git-crysp.uwaterloo.ca/sengler/relay-throughput-testing