Not really a possibility to use anything but an Intel cpu.
Not true. Apple could easily go with an AMD CPU, and use an AMD (no longer ATI) chipset/GPU combo. This would be sorta the "norm" in a sense as Apple really liked the Nvidia chipset/GPU combo. If AMD can provide the best overall solution, I hope Apple goes with it.
The problem with Intel, is it markets to consumers that the only way to improve computers is to upgrade CPUs. In reality, the C2D CPUs are amazingly capable. What we need is for Apple to focus on all of the other things that with tuning could be impressive.
For example, go beyond SATA-II as SSDs are quickly going to saturate the bandwidth of SATA-II drive controllers. The bottleneck in the current computing environment is the drive and drive controller combination. The reason the MBA with an SSD is so very fast is Apple jumped on the SSD bandwagon... and thankfully it didn't take them as long as it has with other tools and components - like no Blu Ray and etc.
Take advantage of better graphics systems. Focus on making simple use of OpenCL and other tools available to application providers. Make Grand Central Dispatch a widely used tool. Keep focusing on software improvements. ADD MORE ***** RAM!
About the least problematic (and most capable) component in the MBA, or any Mac for that matter, is the Intel CPU. But until consumers understand that, Apple will be forced to upgrade the damn things. Just like when it upgraded the 15" to Core i-Series CPUs... the users would have been better off with C2D and Nvidia 320m, as they would have had the much more powerful base graphics system. Everytime the 330GT kicks in it eats more battery than it would have had the 320m had first crack at taking care of the graphics.
I would say people need to learn about the current state of computing and understand what the hell does what... before preaching go big, GO INTEL, or go home.