Almost everything is `promise` based

[cabanier]

Is it necessary that every method and attribute returns a promise?

[marcoscaceres]

As I draft the spec, I'll review review each on a case by case basis. However, as stated in the explainer:

Note the use of promises since it is likely that the model is rendered out-of-process and any communication with that process would need to be asynchronous. This applies to other promise-based APIs discussed in this document

but will check if there are calls that don't need them.