"If you can stand to define a separate macro like 'lazy-amb and use it at each call site, it's a design pattern that obviates most use cases for fexprs."
Indeed. You and I had discussed this quite some time ago, about having convenience macros that expand into thunks. This thunkification is clunky and awful, but it does indeed give many of the benefits of vau.
I still think any new Lisp should use vau, but thunkification is a great way to retrofit many of the benefits of vaus into older (?) Lisps like Arc.
