Uhh... the Xbox 360 RROD issue is caused by the tiny solder balls between the chip and the logic board breaking due to thermal expansion and the poorly designed heatsink mount, not from the heatsink shorting something. If that were the case it would likely happen the very first time the xbox were allowed to get up to operating temperature.
Mobiles yes, consoles no. None of ARM's current designs are anywhere near as powerful as the processor in the 360, and that was launched years ago. I find it very unlikely that their next console will be less powerful than the 360.
Yeah pcs have larger airflow, but because the xbox 360 lacks that does not mean MS cant hire good engineers to build them a console with good airflow. It might have a larger size to it, but it would do the job better.
Just look at those Shuttle PCs, many of them are rather small, yet do a good job keeping their components cool and stable for years.