According to a report by Xbox360Achievements.org, Microsoft will soon be doubling the number of gamerscore points allotted to XBLA titles from 200 to 400, with the maximum number of achievements being upped from 20 to 30.
In addition, DLC will have its gamerscore allotment raised from 75 to 100 pts, with up to four DLC packs allowed during the lifespan of a title. So after all is said and done, any retail Xbox 360 game can potentially net you up to 1,400 gamerscore.
These changes will allegedly go into effect between April 1 and May 31, with games released during this window given the option of adopting the new system or keeping the traditional setup. All new Xbox 360 titles released after June 1 are obligated to follow the new achievement policy however.
Update: This policy has just been confirmed by Microsoft’s Larry Hryb aka Major Nelson on his blog.