It would look pretty much the same. It would just have been written to be multithreaded from the beginning, and lack the long list of restrictions and caveats a

It would look pretty much the same. It would just have been written to be multithreaded from the beginning, and lack the long list of restrictions and caveats and "but it doesn't work with our C extensions" and such. There wouldn't be a dozen major libraries trying to solve the problem (which, contrary to many people's intuition, is often a sign that a language lacks a good solution). This is part of why I say there's no fundamental reason this can't be done, it's just a historical accident.