Facebook has already made that mistake with PHP. They are still paying the hefty price for that. Language popularity at a given time doesn't guarantee a higher ROI in the future. For the next couple of decades, CS experts will be debating over languages that optimized for programmer's productivity, optimized for performance and languages that offer correctness (probably via type systems and other mechanisms). Javascript today doesn't fit any of these categories, and although it is quickly evolving, it still hasn't shifted towards any of those sides. It has become more performant than initially, but yet not fast enough (e.g.: for native apps). Sadly the story is old, happened many times - happened to Joe Armstrong and Erlang at Ericson, that happened at MIT when they switched from Scheme to Python. It happens whenever companies ignore their engineers and arguments they make, but eagerly listen to their Marketing and Sales teams.

Honestly, I would love to see faces of those stupid imbeciles who after hearing all John Carmack's arguments that tool X is making him very productive, later tell him that he cannot use that tool.