It makes me sad that the stdlib will no longer provide a way to compose classmethods with other descriptors. However, I agree that deprecating classmethod  chaining is probably the correct course of action, given the complications this feature has caused, and the backwards-compatibility issues it raises.

This is probably a conversation for another BPO issue or the python-ideas mailing list, but I hope some consideration can be given in the future as to whether a new classmethod-like feature could possibly be added to functools that would enable this kind of decorator chaining without the same code-breakage concerns that this feature has had.