Another interesting subject only slightly touched on here has been the degree to which Perl 6 features have been slowly rolled in to Perl 5; maybe Perl 5.30 will look a great deal like Perl 6.
You don't need to depend on anything from Microsoft for development, I've toyed with TypeScript using Node.js and Eclipse on Linux without issues. And as stated before TypeScript compiles directly to Javascript and they are trying to align their syntax with ES6.
Seems quite kosher. I think at this point if Microsoft tried something shady a community fork is very doable, or if it doesn't happen you can always compile to plain JS and continue working there.
It's really different from the situation you describe because developers and users won't tolerate a MS JS that only works with MS browsers, they have to remain compatible with the others or risk irrelevance.