Like some users said before - Achievement-system should NOT take time off from fixing other issues and polishing the game. However, there are plenty of things that could already be put into motion: exploring, certain quests etc. could grant achievements. Some kind of a system would be amazing, since it would really keep the game alive in a sense (and achievements are indeed optional) and give max level players some things to grind and a chance to feel accomplished by doing certain little things. And when this Achievement-system is implemented, it does not take so much effort to add more and more achievements when needed / wanted since the core of the system is already there.
Achievements are always optional. In my honest opinion more and more players are really longing for a system like this. And the options with this system are limitless: some mounts / titles could be associated with certain HARD achievements or certain rewards could be given for accomplishing some amazing feats. I am really looking forward to hearing some news regarding this from the developers at some point, at least.