It'd be good if nvi was in /etc/mailcap the same way that vim is.
debian/nvi.mime and rules diff below can install
/usr/lib/mime/packages/nvi which mime-support "update-mime"
automatically puts into /etc/mailcap.

These bits are lower priority than vim as noted in the comments, but of
course you might remove vim in favour of nvi or the sysadmin can always
fiddle with /etc/mailcap.order or a user copy particular mailcap lines
for personal preference.