Strategies for offline PGP key storage

One of the problem I've encountered with having multiple signing keys is that not all programs using GPG make it easy to choose which key to use for signing. Last month, for example, I added that signing key and that key took well... about a month to propagate through Debian's infrastructure. That gave me time to notice that:

1. gpg chooses the latest signing subkey (I would have expected it would sign with all available signing subkeys)
2. notmuch-emacs and mutt do not allow you to choose which subkey to use to sign outgoing messages
3. debsign *does* allow you to choose the signing subkey, but that's about the only thing

I had to go back to inline signing to send email... And I had to specify the signing key with a bang ("!") at the end, which was weird and unusual (I would have expected the keygrip to work here for example).

So in short, it's a pain in the back to rotate signing keys, I wouldn't recommend having a workflow based on doing that on a regular basis, unless you control key propagation.