As an active achievement hunter (25445 points so far), I can see the desire, and there are a few achievements such as the IC arena one that can be gotten quickly if several players cooperate (though that may be against TOS, somewhat similar to the outpost trading that recently got several hundred players banned).

The challenge in making a guild around this concept is that many of the achievements are geared toward specialists, such as Maw of Lorkhaj Hard Mode and Grand Overlord. For these sorts of achievements, you're actually better off joining several specialist guilds, rather than a single "achievement" guild, as it is unlikely that a general achievements guild will be able to persist and perform at that high of a level.