Can you describe a bit how you'd envision this to be used? Would there still be a single set of constraint violations at the end, which would receive in a blocking fashion (i.e. only the validation of constraints would be parallelized)? Or do you envision this more as a "reactive" API, i.e. there'd be a subscriber of sorts that listens to a stream of violations?

We had some discussions regarding asynchronous valiation for BV 2.0, this was in the context of UI validation. About the use case I'm not exactly sure whether it's something I'd recommend to implement using BV. Can you maybe describe some more details of it? I.e. where's the URLs coming from, how are the results shown (to a user?) etc.