People don't realize just HOW MUCH room there is inside the Xbox 360. Space that should not be needed for cooling, if cooling is done right.
Original PS3, inside has basically no space inside, and in the slim, none. What sony does right is design this stuff for a few reasons, they know how to cool. The heat sink inside the PS3 is almost 1/3rd of the original PS3, with a HUGE fan at lower RPM, bigger fan at lower RPM does same job as a smaller fan at higher RPM and makes much less noise.
What Microsoft did, was use smaller heatsinks, smaller fans, and a lot of "venting room" this is PC logic, not console logic. They also put the GPU originally underneath the DVD drive, and used heat pipes to direct excess heat from GPU into CPU heat sink thinking that would WORK. It does, however thats where RROD came from. RROD could of easily been fixed, the heat sinks for both CPU and GPU are to small, and the GPU didn't even have a fan on it's heatsink, just heat pipes bringing excess heat to CPU heat sink. They fixed that, moved GPU and CPU, bigger GPU heat sink and I think it even has its own fan now. However that is not enough.
What the 360 should of been, is the CPU and GPU being an inch apart, and the heat sink being the area from DVD drive, to the end of the console. The heat sink could of been about 1/2th inch think aluminum fans, with a single fan for cooling, with heat pipes distributing heat. This would cause all overheating problems to be almost null, with this, and a smaller DVD drive, the original 360 could of been almost 2/3rds the size it is now, in thickness. There is also no reason the power supply couldn't of been included in that same size. Right now, if they wanted to go slim version, they could of shrunk heat sink etc due to 32 nm tech, and the 360 has no reason it could be half the size it is now, WITH the power supply in it.
However why didn't they do that? Cost mostly, microsoft is so cheap they removed a 0.5 cent piece of rubber from the dvd drive, which stops the DVD from hitting the laser, to save money. This is the reason that if you move the 360 with a dvd in it, it'll make a circular ring around destroying the disc. You could of took the console, and shook it when it was on, if they didn't remove a HALF CENT PIECE OF RUBBER.
So chances of slim are very slim, unless they can save on production cost, and by the way microsoft do things what they are going to do is shrink CPU and GPU, shrink heat sinks, and leave console same size.