One way of reading what he is saying is that if you are thinking of using pure FP for your application and it is not primarily a calculator (e.g. Jane Street) then be careful - nobody has proved that it will be quick to prototype, iterable, maintainable, understandable, flexible etc. Surely the academic community should feel more obliged to test their theories and follow things up further than toy examples or examples that match the paradigm exactly? What are they being paid for? In the meantime if someone does want to be at the cutting edge what would be interesting to see would be a word processor, a CAD program or a photoshop developed using a functional language (not a hybrid like Scala but something like Haskell where state is completely isolated using monads or whatever).