I’m not so sure, you have Av and Tv, why not a Iv? It’s the three factors that set exposure. The ability to lock down any two and let the third float just seems to make sense to me.
All DSLRs will have this feature one day..
Now the MkIII has a limited version of ISO shift,. does the 40D not?
I do not think the lack of this feature in other models has anything to do with "flagship"
It's juts simply a new feature that Canon has only recently adopted.
Every newer model will have this feature at least, and in fact it will continue to evolve.
Go back to some of Noinks older models and no they do not all have it. It was introduced in the last few years.
We can not expect all companies to adopt new features at the same rate. Look at how long it took Noink to put IS in there Big Gun telephotos..

