It's a lovely concept. Taking on the UMPCs, which do - in fairness - suffer from hot and hungry CPUs (or just Not Very Good Ones) is a very worthwhile task as the market for these devices matures/converges with PDAs.
But what OS is going to power these? The UMPC's benefit to the consumer is easy, instant access to mature and well-developed (or at least, functional) applications on an OS that they are familiar with. Will the multi-core chip be supported by derivatives of Windows Mobile?
In which case, will we see manufacturers migrate from what is already becoming an expensive platform, where unsubsidised hardware like the HTC Advantage costs £650 for a 256MB ROM, 128MB RAM, 8GB HD device with a 5" screen and a 624MHz CPU that spends most of its time at 102MHz in a struggle to get an 8hr runtime. The same money will, whilst losing the telephony capability, get a 1.2GHz VIA C7-M powered Ubiquio 711 with 1GB RAM, 40GB HD, and Vista which will do about 3 hours of snappier, more versatile operation. Neither device really fits in a pocket for most users, after all.
Will we see Linux, perhaps? Devices that are slightly unfamiliar to the mass market, and at a fair guess will take two to three years to be developed and marketable (remember how long it took for UMPCs to be developed and ready for launch).
By the time this CPU is ready to hit mass market in a UMPC-style device, Intel's 45nm chipsets will be there, LED backlights will be cheaper, HD density will have improved, and who knows, maybe MS will have managed to drum up some enthusiasm for Vista. Where ARM's clever little chips will of course continue to make the world tick and people communicate, I think that Intel and Microsoft's approach to the PDA will ultimately succeed by sheer brute force, by giving the consumer the ability to carry their desktop not in terms of "productivity" but in terms of actual functionality and familiarity. OQO's Model 03+ will be sporting a 1.5GHz variant on Intel's A100 chipset, 2GB RAM, a 160GB HD and an HD screen for £999, FlipStart will be selling the V2.0 with a Core 2 Solo and 80GB HD, and Ubiquio's OEM sources will be mass producing OQO performance in a bigger box for half the price. Sony will probably be shipping 1.86GHz Core 2 Duo systems for £2000, and all of them will have HSDPA or equivalent comms.
Of course the ARM chip would offer theoretically better performance for a given clockspeed, or better battery life, and would be vastly more efficient with a decent OS on top of it... but it's not going to change what the market wants. And the market is still unsure it wants anything at all, but when it does figure it out, it wants "desktop, in pocket".
iPods don't need multi-core. They work perfectly well as they are, and that's not a "no-one needs more than 640K RAM" statement - once the iPod needs that kind of CPU power, it is becoming a new device.
There is one mass market device I can see, and it's mentioned here. If Apple, instead of as rumoured shifting to Intel, deploy this multi-core CPU in an iPod Touch, with more real RAM and storage memory, and a suitable port of OS X on ARM... then perhaps Apple could develop the PDA that does become the device everyone wants.
Before that, I think we need iSync and .Mac support on Windows, and open development on the platform. The question everyone asks is "WIll it run MY apps". Until the answer is yes, very few consumers are interested and only the geeks and those truly new to computing will attempt to work around the limitations to gain access to the hardware. For an Apple PDA to truly succeed, it has to be available to both Windows and Macintosh users.