I've heard that interpolation with existing JS libs is painful.
Another great thing about the community is a goal of a single great library for every use case, rather than a lot of half-baked competing libraries. So expect there to be a single great modal library. Etc.
The only "official" interop channel is the "port" system, which only lets you do a publisher/subscriber type thing with your application at runtime, and cannot be used in a library.
So you basically cannot make a "blessed" library that uses native browser APIs.