Canon holding back 7Dmk2 for a reason. I suspect 100-400 mk2 announcement, or some other coinciding situation.
Silly statement.
Canon could have released a 100-400 II at any time over the past five years or so. Lens technology doesn't change that much and this lens design has probably been sitting around for quite some time, just waiting for the right time to put it into production. There is no reason Canon would need to "hold back" any camera body for a lens.
And, what exactly does "holding back" mean? The implication is that the 7DII has been completed and ready to go for quite some time and Canon has allowed it to sit idle. Hardly a likely strategy for camera technology, which has a relatively short shelf life. Certainly all companies time their releases to obtain the maximum benefit, but that is a matter of weeks or months. To call it "holding back" reflects a gross misunderstanding of everything involved in a successful product launch.