I'm wondering if it could be a move package of some kind. Usually a bundle is the second or third number, but if they've changed the system somehow, it could warrant the first number change. Something like a built in camera or some kind of secondary tracking system.
Earlier this year we saw some patents for a ground camera/receptor. It's possible that they included some kind of bluetooth tracker or something that could also be sold as an accessory.
Another possibility is a different kind of harddrive like a solid state drive, or flash drive. I have no idea. The number doesn't necessarily indicate a slimmer version, but I do think we'll be seeing a 200-250$ ps3 either by e3 or tgs.