No matter how much content they release, you will be done with it way before they have time to create more. That's just the type of game this is unfortunately.

Moving the relic quests to be sooner isn't really going to postpone the feelings your having much longer. Plus, toward the end of Stormblood, there will likely be a decline in subs and extended quests like the relic quests are one of the few ways to entertain the playerbase while you finish up the new expansion.