Hi Sergei,
Thank you a lot for the answers. For my part of questions :) your answers sound very promising, so I'm looking for Q4.
P.S. Actually, at the moment I am not really interested in the scripting support because variables/data selectors in arbitrary places of the request seem to be able to do what I had to implement via scripting and I agree that it is easier to provide tests concurrency with data selectors than with scripting support. And I don't have other good-enough use case example at the moment that can be implemented only via scripting.