Sony filed a patent for a new Game Cartridge, will future PS games be Cartridge based? *****Update*** It appears to be for Toio :(

[Megiddo]

Going to throw out a random guess that their next "portable" will be their Xperia phone that can play games via cartridge. Making a portable game device merged in with their current smart phone line would be the only way I could see Sony re-entering that space.