Speaking in this GI interview, David Edery - worldwide games portfolio planner for Xbox Live Arcade - has confirmed that the file-size for XBLA games it to be extended from 150Mb to 350Mb.
"Yeah, it's a steady progress," when asked if the new size was correct. "We've been listening to our partners, listening to our customers to try and get a feel for what's right. We don't want the size limit to hit the roof because we think there's some value in promoting small pick and play experiences that don't cost USD 20 million, it's good for the ecosystem."
Edery fell short, however, of confirming when the new limit would be put into effect.