I propose to drop support of "Vacation" in favor of standardized SIEVE (RFC 3028, RFC 5230, RFC 5804, RFC 5435) that support vacations auto-responder in addition to very powerful filtering mechanism.
SIEVE already supported in major email's clients (Thunderbird, RoundCube, Horde and etc) and allow much more flexibility to assign Vacation response(it could be special rules to avoid respond to robots, or other auto-responders/notificators)
SIEVE supported very well by well known Dovecot, Courier for a long time and actually it will be better to leave actual mail delivery to primary servers instead of custom, non standard Perl's spike.
So, IMHO it would be a good step forward in 3.x development to drop custom, non standard Vacation support in favor of supporting SIEVE language.
Since postfixadmin allows regular users to manage own settings, it will be good to implement in a future web based SIEVE's rules management via postfixadmin in manner as it done in INGO application from Horde framework for example that bring a lot of power to users and administrators to manage Vacation, Spam filtering, forwarding, black/white listing and much more without actual need to learn SIEVE language...