[beggi]

Eliminating nested callbacks would be one hell of a feat.

[lalc]

It's not too too hard to do the appropriate transformations--the literature is vast and there are practical implementations today. The hard part is producing readable, debuggable output.

I've whipped up a tiny project with the priorities inverted: readable output at the expense of completeness: https://github.com/lalcmellkmal/nestless

It only does the minimum desugaring to prevent nesting in the common case, no more.