It is a clear case of the license hampering the adoption of an otherwise good idea (JSX is so commonplace now, Opa had it already in 2010). But you are right, the actual close source era of Opa was very short.
i would wager that c# standardizing it's specifications (over ten years ago) and having an open-source implementation (mono) was a big deal, and moving toward rosalyn was certainly a strategic move.
#11 is Delphi/Object Pascal.
MATLAB.
Not much else.
Because of FPC, arguably, if you use Delphi you're not exactly stuck in the unlikely event that it dies since in the worst case there is Free Pascal to move to, LCL and Lazarus (although I have no idea how it compares to modern late 2010s era Delphi and RAD Studio but it's at least something). Delphi also has a more or less proven track record, costs a lot, is pretty much enterprise tier item and has a multi million company behind it.
I'd argue Object Pascal is not a closed language but a language that has few implementations, one major open one (FPC) and one major closed one (Delphi) and that the situation is even better than C# vs. Mono was, since Mono had a murky legal/patent situation (or maybe it was FUD, I'm not too into C#) and the situation was basically 'closed language with a closed implementation that happens to have an open implementation' while FPC and Delphi are more like brothers with Delphi not 'owning' the concept of Object Pascal in itself nor any patents that could threaten it in any way AFAIK.
https://github.com/dotnet/roslyn https://github.com/dotnet/vblang