Strategies for offline PGP key storage

That's true. But for example Debian encourages to use signing subkeys, see https://wiki.debian.org/Subkeys (although not explicitely short-term keys). But in the end I guess you'd only have to wait until your new signing subkey has landed in all keyrings and let your current one expire, which is solved by overlapping the key validity intervals by a few weeks and always using the oldest.