I have no inside info - just guessing based on technology and Canon's other products.
Recall that the G12 was introduced together with the S95 (the predecessor to the S100). So the G12 is now 2 generations old.
I think the body size, lens, and ergonomics of the G12 are already pretty good - I can see why Canon doesn't see a need to change them.
But I think we'll see the G12 replacement (G14, at a guess) has the CMOS 1/1.7" sensor from the S100 (or slightly newer), DIGIC 5, improved movie mode (1080p/60 would be great), and the high-speed movie capture from the S100 (200 and 400 frames/sec).
I hope it'll also have GPS (again like the S100) for geotagging.
And maybe, maybe, if we are very lucky, it'll have hybrid phase detect/contrast detect focusing (like the latest Rebel). That would mean a huge (and much-needed) improvement in focus speed.
If it has even 2/3 of those, I'll buy one the first day it's on the market to replace my G11. I've been waiting a long time, and the G1X isn't what I'm looking for.
If I'm right, externally the new camera won't look much different - same body, lens, controls. But inside a lot of changes that matter.