The Web-Interoperable Runtimes Community Group

a) Divergence in implementation on the same API surface (e.g setTimeout in Node) b) Divergence in API surface for a similar implementation (e.g WHATWG streams vs Node streams)

The former is obviously much harder to change than the latter, as the latter can be resolved by adding additional API surface. I assume you are talking about the former.

This sort of divergence where implementation differs, but API surface is the same is luckily pretty rare. The most prolific example is setTimeout in Node. It's unclear how exactly the Node project intends to deal with situations like these. It's possible that this is something which can just never be solved in Node, and it just sticks around as a "wart" forever. The solution to compatible APIs for cases like this would likely need to be a new API then. For async timers this could be a promise based API like `Promise.delay()`.

There is unfortunately no "one size fits all" solution for these problems though, which is why this CG exists. We're going to try to categorize and come up with solutions to these problems.