Re: not happening - Unless one could remove the thin display (tablet?) and take that with. Tho I suppose that would require a much larger media event than it appears we'll see. Was just a fun and unoriginal prediction.
Re: defeat the concept of the iMac - Huh? If the concept of a iMac is "all-in-one," then my prediction stays true (with a twist).
Regardless, newsflash - thin is in (hello over priced and poorly spec'd Samsung LED TVs or iPod touch or...). When it comes to electronics, current consumer spending trends seem to suggest they care more about the thinness of their devices than performance. Which should fit perfectly in the iMac target demo's wheelhouse. This demo surfs, email, chat, Word, iLife, iTunes, etc. And these user habits are easily met with a laptop-grade processor. Thus, I fully expect thinner iMacs.