What's not supported is the current draft proposal for standardized ECMAScript decorators; if you uncheck experimentalDecorators, the decorator syntax is simply passed through as-is, even when lowering to ES2015.
Awesome. Standard decorators support is not a dealbreaker for me, but enums and other types of non-erasable syntax would be.
Do you know what the status is on using Rolldown as a crate for rust usage? At the moment most rust projects use SWC but afaik its bundler is depreciated. I usually just call into Deno for builds but would be nice to have it all purely in Rust.