I'm claiming that using self-recursion just makes sense. The inability to have a recursive implementation of fib(n) is a loss in both expressiveness and readability. Recursion is fundamental to computer science, and is often the best way to express many types of operations. So, in my opinion, if Guido really wants Python to be simultaneously readable, expressive and pragmatic, TCO is necessary, because recursion just plain rocks sometimes.
Edit: You and Guido are in agreement. It's a "feature" in that it visibly affects behavior, whereas an "optimization" would merely make things faster.