As the talk mentions, Jython (Python on the JVM) is living proof that it's possible: it doesn't have a GIL and it works just fine.

The issue is "just" one of implementation. Sun and Oracle have spent millions of dollars paying ridiculously-smart people to make HotSpot as good as it is... while the CPython codebase has traditionally aimed at being simple enough for average C programmers to contribute to. I'll be interested to watch how that tension plays out.