The default right now for the non mp-* import, export, etc is to
assume ipv4-unicast. Maybe what you want is adding the option to the
existing non mp-* syntax to specify other protocol. What might be
better is to keep the idea of mp-* but make the default protocol
ip-everything ({ipv4,ipv6}-{uni,multi}cast). At the very least we
need an ipv4-all and ipv6-all. The ip-all or ip-everything would be
shorthand for ipv4-unicast,ipv6-unicast,ipv4-multicast,ipv6-multicast,
which is a lot to type. If a lot of providers have common policy then
omitting any protocol spec could default to ip-everything.