Mojo's promise is the same code, but faster.

They were planning some language extensions but it's more like a compiler project than a programming language project.

The truth is, most developers don't want to learn a new language.

They will jump through extra hoops just to use their favorite one (e.g. Airflow).

Successful languages appear when there is an extreme market demand (C++ providing OOP over C) or, more commonly, a hot new platform that people want to get in on (JavaScript, Swift, Kotlin, C#, ...)

For most people, new syntax / semantics is considered a negative and there needs to be some massive upside to overcome that.