UPDATE: It's official, kids. Major Nelson confirms it. Carry on.
ORIGINAL POST: The number of Xbox 360 Achievements and total Gamerscore boost that developers can offer on Xbox Live Arcade and through related DLC will soon be changing, an Xbox360Achievements.org report from an unnamed source reveals. If the source is accurate, the new rule will go into effect for all releases on June 1 of this year, with developers being given the choice of working within the old system or the new one from April 1 to May 31.
Under the new framework, Xbox Live Arcade titles will be working with a total of 400 Gamerscore, up from 200 GS, and a max of 30 Achievements, up from 20. Downloadable content for these games will now be able to offer an additional 100 GS and eight Achievements per release, with one allowed per quarter. Overall, you're looking at a potential total of 800 GS for an XBLA title, and a total of 62 individual Achievements. Bear in mind that this is a rumor; we're checking with Microsoft for comment.