What makes WebVM (and CheerpX, the underlying virtualization engine) different is the level of performance that we have achieved.

Although CheerpX is not yet perfect and additional optimizations are required on its floating point and vector pipelines, it's already fast enough to be practically useful on many use cases, especially when legacy/older binaries are virtualized.

Which WASM features does CheerpX use? GC, BMO, Branch Hinting, Relaxed SIMD, Threads, Memory64?

CheerpX uses SharedArrayBuffer, which is associated to threads, and can optionally use Branch Hinting if available. The latter is fully standardized, but not yet enabled by default in Chrome.