The 'appliance laptop' market is too similar to the failed netbook market for Apple to approach or care about, I think. If Apple were to come out with an new or hybrid category I don't think it would resemble an 'appliance laptop'.

Afterall, the MacBook Air wasn't a competitor to the netbooks - it was a competitor to the ultrabooks being touted by Intel et al. The iPad was the sleeper competitor to the netbook and killed that market (with help from Windows and Intel desperate to not have the PC platform not go that far down market).

If Apple comes out with something to address the 'appliance laptop' market I expect it to be an official Apple design and manufactured keyboard for the iPad line* and not an entirely new product.

I've not seen it mentioned anywhere yet, but the "iPad Air" and "iPad Mini" monikers leave room for the simply "iPad" moniker to eventually refer to something entirely re-imagined or ultra-premium. At the least it leaves room for a larger "iPad".

* What is the state of the art in usability in the 3rd party iPad keyboard market these days?