The feasibility of contact tracing has nothing to do with the R. It's practicality is purely based upon your ability to contact people who are infected. Sure,

The feasibility of contact tracing has nothing to do with the R. It's practicality is purely based upon your ability to contact people who are infected. Sure, tech tools that automate part of that process, increase that number - maybe even benefit more rural place - but if you launched it in NYC right now, it'll just notify literally everyone in the city, day one. That's not useful.