To me it seems that it is quite likely the next xxxD will have the same sensor as is in the 7DII. If they bring it out before the 7DII then maybe they think it will eat away some of the 7DII sales from the people that have a 7D now and are just looking for a camera that produces better IQ (and not necessarily better fps/AF) whereas if the first camera that 7D owners see with the new sensor is the 7DII then they stand to get more carry over sales from people who see it and say "I WANT!" (or at least that's my thinking, feel free to point out where I'm wrong.) So new sensor in new 7D model, maximise profits from upgraders buying new expensive camera that they may not need but want.
Now had they of released a new xxxD camera a month or two ago with existing sensor technology and then a few months later the 7DII comes along with a new sensor then maybe they're afraid that sales of the xxxD will stall because people will wait for xxx+1D from Canon with the same upgraded sensor tech that is in the 7DII. That would also prevent them from releasing a new xxx+1D that uses the new tech in the 7DII in the first half of 2015 because it would be too soon between models. It won't necessarily matter what is new in the 7DII just that the 7DII will have all the new stuff and people will want the new stuff in cheaper bodies and may delay purchasing decisions because of it.
So a bigger gap between xxxD models (no real problem with sales) so that they can slot in the 7DII and roll forward with whatever new goodies (new DIGIC too?) come in that.
Sound like a reasonable plan or am I just crazy?
I think you are right!
Its a typical policy for all manufacturers, and Canon is nothing, if not consistent and conservative in their operation.
However, with DSLR sales dropping, Canon may just not want to turn out new models as fast. A new model, even if it only has a new badge on it costs a manufacturer a ton of money. Old stock must be discounted, advertising materials and media must be updated (It costs a lot of $$ to make new TV commercials). The cost of stocking warehouses with a rebadged product is also high, they have to build cameras at full speed for 3 -6 months to get them in the pipeline. Doing this every year is a business expense that drags down profits, and if it does not generate enough new sales to make a good ROI, Canon won't do it.
Canon had stated (about a year or two ago) that a new 7D would only come out when there was a significant upgrade, obviously, they have been working at finding better technology that is producible at a target cost and sell for a big profit. Once they skim the cream off the early adopters, the upgrades will trickle down to consumer models, and some of the advanced tech held back from a 7D will appear in the high end models.
Canon is very predictable.