It would be great if assword supported multiple keyids for encryption, so that
it could be used to make a shared password database file among a number of
recipients (for example, in a shared git repository).

I think that the easiest thing to do would be to allow for multiple entries in
the ${ASSWORD_KEYFILE}, either separated by commas (or whatever is easiest).

Additionally, when the target keyid is not present, assword could change its
prompt to indicate multiple keyids, instead of:

micah@muck:~$ assword add
OpenPGP key ID of encryption target not specified.
Please provide key ID in ASSWORD_KEYID environment variable,
or specify key ID now to save in ~/.assword/keyid file.
OpenPGP key ID:

it could be:

micah@muck:~$ assword add
OpenPGP key ID of encryption targets not specified.
Please provide key IDs (separated by commas) in ASSWORD_KEYID environment variable,
or specify key IDs now to save in ~/.assword/keyid file.
OpenPGP key IDs: