The DBI lets Perl happily talk with virtually any RDBMS backend, such as MySQL, and this is good.

The DBM facilities provide a lightweight and ubiquitous solution for where an RDBMS solution would be overkill, and this is good.

I really don't see why DBM support should be 'dropped' in favour of database backends, both coexist happily and complementarily. Removing DBM code won't automagically improve RDBMS support, it'll simply mean people who do deal with DBM files will move to another language.

A final point, DBM files are exceptionally standardised, and have been for many years. This stability means having it in the Perl core distribution makes a certain kind of sense since the code will Just Work, whereas trying to put (for example) a MySQL DBI module into the standard distribution wouldn't work since there's versions of MySQL arriving too quickly, and it won't really help those of us sitting next to the big metal Oracle.