To continue my journey of reviving decade+ old Perl code, here is a fully Webmin 2.x compatible version of the vsftpd module (Magic Wave version).
The changelog as compared to the 2009 release is:
Overhauled to work properly with Webmin 2.x
Default to use systemd commands to manage the server daemon
Replaced the tabs navigation UI on the Main Configurations page with a plain table layout
Add module icon (only used by the Legacy theme)
Removed external link to a now-defunct company website
Hope this is useful for someone out there!
As a side note, there is also the vastly different Nick Herrmann version (last updated in 2010) floating around on the internet. I decided to work with the Magic Wave version since it had a tighter feature set and less obvious bugs.