I have zero hesitancy to blow away a git ssh key for any reason and use different keys from different hosts which are not used for anything else.
Entangling an ephemeral key as a supposedly permanent signature would have to be for things I had no long term commitment to.
I'm a little confused. I thought this was how you're supposed to do it, so you can easily revoke access for a particular host.
Which is why this is a bit silly and I don't see why you'd do this rather than "good old" PGP.
Why can a PGP key be permanent but an SSH key not? I'm assuming both are just files and as a user you are required not to lose/give them away.