Comment 3 for bug 1718227

$ apt show plan netplan | grep -A 3 Description

WARNING: apt does not have a stable CLI interface. Use with caution in scripts.

Description: X/Motif day planner
 Plan is a schedule planner based on X/Motif. It displays a month calendar
 similar to xcal, but every day box is large enough to show appointments in
 small print. By pressing on a day box, the appointments for that day can be
--
Description: network server for `plan'
 Plan is a schedule planner based on X/Motif.
 .
 Netplan adds to plan multiuser capability using an IP server.

This doesn't sound like the sort of thing to replace ifupdown... some more information about what this actually refers to would be helpful.