I think most async runtimes give you the option of launching a single-threaded executor when you explicitly request it.

AIUI the most esoteric tradeoffs wrt. GC involve how to have data representations that can be efficiently traced, and whether you should allow e.g. moving data in memory as part of the collection phase. But I think you're overestimating somewhat the variation within the Rust-focused community - given what most Rust code looks like, they're going to be mostly interested in something straightforward yet efficient, that can interoperate with existing Rust code w/ relative ease while addressing the common issue of cyclical data references.