This is what Swift does, and it has even lower performance than tracing GC.
(To be clear, using RC for everything is fine for prototype-level or purely exploratory code, but if you care about performance you'll absolutely want to have good support for non-refcounted objects, as in Rust.)
An interesting point, but I would have to see some very serious performance benchmarks focused specifically on, say, RC Rust vs. GC Golang in order to entertain the notion that an RC PL might be slower than a GC PL. Swift isn't, AFAIK, a good yardstick of... anything in particular, really ;) J/K. Overall PL performance is not only dependent on its memory management, but also on the quality of its standard library and its larger ecosystem, etc.
