I'd like to share my gpg.conf between multiple machines. It seems entirely
machine-independent, except that it has the key-specific default-key and
encrypt-to options. While a user with a single private key could omit
default-key and gnupg would guess correctly, Werner Koch suggested that users
should not do that, as it makes gnupg less robust, such as if another private
key gets imported.

To solve this problem, what if default-key took a list of key IDs to try? It
could then select as the default key the first key ID for which gnupg has the
corresponding private key. That would allow a single configuration that said
"If I have my secure private key, use that, otherwise use my somewhat-secure
work key."

I will file a separate issue about solving encrypt-to.