Not spring. Canon has to milk buyers with the 7D2 for a year or so. If they released 5D4 with 7D2's AF feature in spring (5 months after 7D2 got released (not introduced)), who would buy the 7D2, if the 5D4 offers same or even tweaked AF with slightly lower frame, but better IQ?
I find it strange they haven't introduced a new rebel yet. It's been 18 months now.
I disagree with you on this point.
Those looking only for one camera, namely a 7D2, are not the target market for a 5D4. One is 2x the price of the other. However, those dropping 3600 for a 5D4 can also afford the 1800 for a 7D2. Also, they are two totally different formats/tools (crop&speed vs. full-frame&sensitivity). The extra reach of crop, vs. the creative capabilities of full-frame are huge factors to many pro buyers that cannot be ignored; saying it is just speed vs. slightly better IQ is an oversimplification of what the two bodies offer.
In short, the 7D2 won't effect sales of a 5D4. Buyers on a budget looking for one camera will get a 7D2. Pros with the budget for a 5D4 will either get only a 5D4, or both a 5D4 and a 7D2. They are a dangerous (ie, perfect) pairing.