The achievements in this game aren't anything special. They're just given for naturally following different paths.
Anyway, any time spent coding achievements is time that could be spent improving the game, so I think it would be a waste of time to make more of them... although you can be sure that the expansions or DLC will each have their own achievements.
Well to be fair, most of the the achievements are handled by a single line of code at the end of a quest, at least that's how it was in Oblivion and Fallout. But I don't give a damn about the achievements anyways. It's much more fun to do the quests or to just go on your own adventures than off chasing arbitrary points, imo. For me, they are there when I start to get bored of the game.