I think that there should be community based achievements and in-game task achievements. Since both are key parts of AG, users that are active on either or both sides should be able to obtain their recognitions.
In-game achievements are planned, but community involvement will be rewarded with Reputation instead of achievements.
In addition to just achievements, perhaps some armatars that are only available through community based achievements and others for in-game achievements would be a nice plus. For the in-game task based achievements, I think that developers should be able to create avatars(which will have to go through inspection by the AG staff) and have them as rewards to those who obtain the achievements of their games.
See above for community based achievements, but for in-game achievements, I think there will be game-based armatars which may or may not be unlocked through achievements.