Quote: APS-C sensors are here to stay. They will ALWAYS be cheaper to manufacture so the entry level Bodies will always have APS-C.
I'm sure the makers of 1/2-frame 35mm film cameras (like my old Canon VFs and my late lamented Olympus Pen-FT system) also thought the format would last. Half-frames thrived under specific economic conditions, then died when domestic (Japanese) consumers wanted (and could afford) MORE. APS-C is basically 1/2 of full-frame. How long will it be sufficient for 1st-world consumers?
Digital sensors, being IC chips, are subject to Moore's Law, where semiconductor costs per capacity drop roughly 50% every 18 months. We've seen that with PNS digicams, where US$150 bought a 1mpx cam in 2003 and a 10+mpx cam in 2008. The equivalent to the 14+mpx sensor on my US$1100 K20D body would have cost US$14K a couple years ago. And a couple years ago, entry-level DSLRs were 5mpx and expensive; now they're 10-12mpx and rather less costly.
The trends are clear. By 2010, the entry-level DSLR will have a 20-25mpx FF sensor, and the body will retail for well under US$1K. Will there still be a market for APS-C DSLRs? Yeah, but it'll shrink into improfitability. Lenses aren't semiconductors (yet) so their prices will stay relatively high, which means that a APS-C half-frame (HF) system won't be price/performance competitive with a FF system. By 2015, HF DSLRs will be a small fringe market for those unwilling to give up their pricey DA* lenses.
And I expect in around 10 years to see glass lenses start to go away, replaced by adaptive-optics chips. Every photosensitive CMOS junction (or maybe small clusters of junctions) will be individually frequency-tuneable and aimable. Every 'lens' will be a pancake, upgradeable with new firmware. I SEE IT ALL NOW! Then of course we'll eventually just have digital taps placed in our optic nerves... but that's another discussion.