I would never develop software on top of a proprietary language that I have no control over. The only way I would consider using a closed source language would

I would never develop software on top of a proprietary language that I have no control over. The only way I would consider using a closed source language would be if there was a source available contract with some sort of "you own it perpetually if we ever stop supporting it" clause. (Who knows, maybe they have that)