That's a completely reasonable approach (although I personally would choose something other than Python as my base). In fact, a bunch of languages do this alrea

That's a completely reasonable approach (although I personally would choose something other than Python as my base). In fact, a bunch of languages do this already--most any JVM language (especially ones unique to the JVM) and .NET language take most of their standard libraries from Java or C#. The fundamental problem with this approach is that either your language is too different from the host for the library to map perfectly or it's too close to the host too be terribly interesting.