There is already Haxe which is free and compiles to a lot of things.
A language for the ages would be a Forth imho; you can write the language on the back of a beermath and it takes mere hours to implement on whatever system.
Currently no, but the progsbase language is very simple and contains only well-known constructs. So creating a compiler is very simple, it would take only a few days. This is like the point you make about forth, except forth contains less well known constucts.
> open source
The progsbase specification is also open: https://docs.progsbase.com/