Well, there aren’t really many details offered or required really, but Microsoft today, via Major Nelson, confirmed that Achievements and Gamerscores for Xbox Live Arcade titles are undergoing a bit of a change beginning in April.
Developers will be able to offer up to 400 Gamerscore points soon, up from the current cap of 200 points. Each game can also feature up to 30 Achievements as well, to divide those 400 points among. By June all games will be required to follow this new guideline, though developers are free to implement them as soon as April.