The ranking system was reworked to help with organizing guild events. Elders are now sub officers and organizers, what they organize is not as important, be it PvE or PvP, as the fact that they try to create and lead events for the guild. Reapers are now the people who participate in guild events, again PvE or PvP, maybe they are members of the raiding team, or of a guild PvP team, or just come to every event that is organized. Veterans are members who have been in the guild for a while but don't participate much, if at all. If a reaper signs up for a raid and doesn't show up, after a few offense they will be demoted from reaper to veterans. Being a reaper implies that you are dedicated enough to show up to a raid you signed up on.
This is not really a demotion as much as a side grade. You, or anyone else in your situation, was not demoted for any kind of infraction but merely because we changed the ranking system.