The biggest problem I had with forced promise asynchronicity was with browser promise polyfills, which use setTimeout to force success and error handlers to be called asynchronously.

This is fine, unless you're:

1. Modifying the DOM and hoping to avoid jankiness 2. Trying to work with popup windows, in a browser which deprioritizes setTimeout in all but the focused window.

I ended up implementing https://github.com/krakenjs/zalgo-promise to get around this. It intentionally "releases Zalgo" by allowing promises to be resolved/then'd synchronously, but my belief is this doesn't have to cause bugs if it's used consistently.