Most of my projects I wound up switching from RxJS to xstream [1], for several reasons related to size/performance and synergy with a framework I heavily use (Cycle.js). It's RxJS influenced, but written from scratch in Typescript with a much simpler API surface and somewhat easier to reason with semantics (default "hot" and "shared" Observables versus default "cold" and "unpublished" Observables).

Also, Typescript now supports (since 2.3) downleveling async/await all the way to ES5, which is very handy.

[1] http://staltz.com/xstream/