Correct, and it is also not 2.6. Breaking perfectly working (and more to the point, non-complaining) code, even if it is for a good reason, is bad. It means, for instance, that I can not upgrade Python on any of the servers I manage, where Python gets used by clients. This is not a hypothetical problem, I've had it happen too often (although fortunately not often with Python, because of the sane policy on backward compatibility.)

If 2.5 warns and does the old thing, the upgrade path is easy and defendable. This is also why there are future statements -- I distinctly recall making the same argument back then :-) The cost of continuing the misfeatures in struct for one release does not weigh up to the cost of breaking compatibility unwarned.