[dj-wonk]

I'd like to see more projects consider this approach for updates.

Would anyone like to share other examples of this sort of thing (such as in other compilers or tools)?

[steveklabnik]

We took a lot of inspiration from C++ and Java, both of which have some sort of flag that says “compile this against a particular version”.

[mlindner]

Except C++03 isn't getting any more features added to it and neither is C++11 (which also use the year, not version number). 2015 edition will continue to get new features.

[steveklabnik]

Yes, the non-2015 editions are direct analogues, but 2015 is special.