It's a much argued point but RISC processors are generally considered to be better suited in compact and embedded systems. Lower power consumption and smaller for the same kind of performance and adding extra peripherals and functions is also simpler for manufacturers than with the quite strict x86 configuration.
The Motorola processor in pre-intel mac's was a RISC (when they really where better suited to multimedia than PC's), as is the core used in the playstation3 and IBM's servers, add SUN systems to that list too etc etc.
That's the trouble, right there. Which one of these systems runs windows? None. The only version of windows that runs on architectures other than x86 is CE, kind of limited choice there. This has fixed the majority of PC hardware development on the x86 path and while x86 is very well suited to a general range of tasks it doesn't allow much room to build hardware with defined requirements or for choosing the path of least resistance in development. As I mentioned above, Motorola mac's really where better suited to multimedia than PC's, as where Amiga systems.
If the cheap, compact laptop market does grow as much as eee sales suggest then we could soon see IBM's core processor being used in ultra-compacts and heavy development of RISC cores from competitors.
It would also leave room for more task specific systems, mac already knows the multimedia business and the BSD base they use runs just fine on existing RISC systems with unusual hardware. But if they can take off in the consumer market then MS will be playing catch-up and will be facing the kind of driver nightmares open-source developers have been dealing with for years as they try and cover a much wider range of hardware and communications layers. Personally I don't think it would be possible for them to compete using a closed source OS, there are too many kernel specific issues for them to addapt to every kind of hardware.
That would put computing back into the kind of situation that existed up to the early 90's with a range hardware and operating systems on offer. A good thing from my point of view but it would make choosing and upgrading systems more complicated.