I'm not sure that's a fair description at this point. They have distributed some SDKs at this point.

I really do wish it were open source already though. I know they have laid out a roadmap for opening the source.

The person in charge of Mojo was previously in charge of a massive effort to give tensorflow a new backend, for which he conveniently picked Swift (a language he was also involved in), despite there being better options, only to abandon it halfway through because it was intractable and Swift wasn’t ready/willing to support the compiler changes needed, so he just abandoned it, and now works on Mojo.

It gives real “Jony Ive leaving Apple to go work somewhere where nobody can tell him ‘no’ “ vibes.

You don't consider developing llvm as an accomplisment?

What other private company languages are there? Swift is the best example I can think of, which matches Mojo's situation down to the head of the project.

aren't most languages invented and initially developed within a private company? Go, Dart, Java, JavaScript, C#, F#, VBA, Kotlin, Erlang, C(at AT&T), Rust (at Mozilla). The list is probably very long

Most of those are open source, and while initially developed at a private company, most are run by non-profits (such as the Rust Foundation for Rust). Also, the language itself is not usually the main product at those companies.

K is one such language.

Mathematica

IBM has some, ABAP, ...

Matlab

MATLAB® by MathWorks