1’’ seems to be the absolute minimum for compacts, since now even smartphones carry sensors this big (cf. Nokia). Compacts with sensors this size will be able to thrive for few years (see the Sony RX100’s success and the last interview of an Aptina exec on DPReview) before having to embed a bigger sensor, like a 4/3 sized one.
Such rumours are already floating around.
Meanwhile, the Pentax Q and Nikon 1 will have long disappeared. They are already dead, and they were a mistake to begin with. The Nikon especially, which stands no chance against the likes of the NEX and XM-1 which aren’t much bigger yet carry a mighty APS-C sized sensor (and – wait for it – the NEX-FF is right in the corner). Too big a body/lens ratio? Then the venerable µ4/3 is at hand. At least the Pentax Q holds some value as a toy.
The next wave of non-system compact cameras will be RX100 competitors. Good thing. Sony is milking us too much for being the sole player with a solid offer in this segment.
Now I wonder. How will the RX10 look like? In-between the 1’’ zoom RX100 and the FF fixed 35mm RX1, are they going to give it a mid-size sensor with a fixed lens? Like... 4/3-ish sized with a collapsible 50mm?
I hope Sony will continue to be daring with its RX series, the market needs it... and so does the company, since its DSLRs aren't that successful. Though, given Sony's lack of customer commitment, I hope even more that Fuji will come up with something interesting. They too have the flair for innovative products, as demonstrated by their comeback with the X series; and they, on the other hand, also release firmware updates in a timely manner.