Currently we are using a beta version of RxJS. In the Release Candidates they have essentially end of lifed AMD support. We can still continue to use the UMD version of the kitchen sink minified files but even rx.lite.min.js is 81kb minified. Given the only real surface area of RxJS we actually use is the Observables part it seems like it'd be trivial to just implement the ES Observables spec as is in TypeScript.