I posted about this in another thread but I can't believe it hasn't really been picked up at news...they kind of sneak announced a pretty big megaton at GDC during one of the dev day talks
They announced "Xbox Live Web Games" which are fully supported by leaderboards achievements etc. Each can can have 5 to 10 achievements total up to 50 gamerscore. Of course the games will still be selected just like XBLA games are, but the technology of building a web game is certainly a lower barrier of entry than building an Xbox Live Arcade game is (with all the technical requirements you have to pass there).
The only place the slides seem to be posted at is here (the slides are in English of course):
http://game.watch.impress.co.jp/docs/news/20120307_517055.html?ref=twrank
Quite frankly some of the games I like playing the most lately are more like match-3 or casual games, it will be great to be able to earn achievements for playing them (probably will work from a Windows 8 tablet too) and many of them will be free or at least F2P. The downside is definitely more expansion of the F2P model where you have to buy $29035133 worth of Snoopy Bucks to complete your little social world.