The idea of a "maintained" V8 is a bit of a myth -- there really isn't such a thing. Mostly, when V8 breaks node.js (e.g., by changing/eliminating a C++ API or by implicitly or explicitly breaking debugging support), node.js has to change. In that regard, it just takes a while to get a version of V8 fully integrated and operating correctly on all platforms -- and I think it would be valuable for the core team to blog some of the history and technical details here...

That's not true and the v8 team's stance is pretty clear. The master branch is the only "fully supported" code base, currently at 4.2.56 [0]. Most other tagged versions going back a year or two receive best effort support. Usually, that means Ben Noordhuis, but often Andreas, Yang, Vyacheslav, and others on the v8-users and & v8-dev lists. Good responses all around in general. And the list of responsive people continues to grow.

[0] https://github.com/v8/v8-git-mirror/tree/4.2.56

The io.js team is working alongside the V8 team to make sure that the upgrades are as easy as possible.

Rod Vagg has a project called NAN[0] to try and allow node modules to compile across node versions.

[0] https://github.com/rvagg/nan