Narrowing down on a single library is one thing. Maybe case by case it's ok. In general if someone showed up and said "I will prototype everything in lisp and you can take it from there" I'd say they are a bit egotistical and not being much of a help to the org. Prototypes are 1% of the work.

And I say this as someone whose full time job was to do research prototypes of robotics libraries for a while.