There already is a loyalty system in place, it's the Veteran Reward system, that SE later neuteured because so much time had passed since launch it was virtually impossible for new players to get the then latest rewards, so most were added to the achievement NPC and became purchasable with achievment points instead.

The Veteran Reward system is based on time subscribed rather than actual time logged in game though, which is deliberate, for the reasons mentioned in posts above, it would only encourage players to sit idle and not do anything, and potentially congest the servers even more than they already are. So you are not going to see any rewards for time logged I'm sorry to say.