I've found an interesting rumor from June.
Now, it seems pretty plausible after that mirrorless patent came out.
Might make sense.
The EOS line has to date had three nominal frame sizes. It might be that the New Canon Thing (NCT) would also embrace bodies of differing format size, with something like 27 x 18 mm (32.44 mm image circle requirement) being the largest (0.75 of full-frame 35-mm format).
I have made no attempt to ascertain the design limits relating image circle to to such things as mount throat and back flange distance, so I'm in no position to opine on the design credibility.
I'm pretty agree with you.
The new "NCT" might be a kind of a new EF-C (compacted or a EF "downsized").
If we look at the proportion, the new flange back distance (30mm) vs EF flange back distance (44mm), is approximately 70 percent of the actual EF flange back (30/44=0.68).
The sensor surface of an APS-C(x1.6) is ALSO 70 percent of an APS-H sensor surface.
APS-H size (in millimeters) : 27.9mm*18.6mm= 518.94 squarred millimeters
Canon APS-C size: 22.3mm*14.9mm=332.27 squarred millimeters
APS-C/APS-H ratio = 332.27/518.94 =0.64
It means, that we can consider these new system as a mirroless EOS sytems in reduction, with a reduction factor of 30%.
It also means, new lenses, design for an APS-H (33.53mm image circle) coverage, smaller than EF Full Frame lenses of at least 30%.
For example can you imagine a 24-70mm F/2.8 L equivalent, that would measure 85mm in length and 58mm in diameter instead of 123.5mm (length) and 86.45mm (diameter) with the same performance and even lighter??
IMHO the APS-H (x1,3) is the first choice for this new mount, at least for the high-end, RF style (with EVF or hybrid), pro bodies.
Thus EF-S lenses + adapter would work on a cropped mode (~70% of available pixel).
It would give 10.3Mp from the actual 16.1 APS-H sensor of the 1D mk4. It's not the best, but it's quite acceptable (remember that it would be the only solution to recycle EF-S lenses, in the other hand it would not be the optimal use of the new mount abilities and it would help Canon to sell new mounted lenses and existing "FF" L lenses).
At the lower-end, canon has just to keep actual APS-C sensor for this new mount, and make "Samsung NX" alike bodies with built-in EVF or something with pellix.
I don't believe in the introduction of a smaller than APS-C sensor, a 18*12 sensor doesn't make sense at all with such a flange back, unless they keep a mirrorbox, but they won't and it already exists ( Olympus E-volt DSLR series, such as the e-620).
Plus Canon would put some money in R&D for a new type of smaller sensor. They don't need to do this, they already have all the materials and technology to create a new mount almost effortless.
And who cares about the aspect ratio in the entry-level consumer range ?? There's already Samsung nx and nex against 4/3, plus with APS-C (x1.5) (slightly bigger than those of Canon).