I don't think it would do anything to ipad markets. I have an iPad and I would never use my 2 in 1 dell system for that. It's just too big and heavy. However, while editing and creating on my dell, I love the pen, touch and interaction of it. Apple, I think is missing the point and the boat. They are only thinking in "the sky is falling iPad would die" scenario. Not the ALOT of new customers would buy macbooks with 2 in 1 design and touch implementation.
As mentioned before, watch snazzylabs video on the macOS touch topic. Apple has already made "touch" modifications to MacOS, it's just a matter of time IMO. They have been behind the 8 ball in this regard and it's time!
Oh, as for adding EVERY feature...A touchscreen does not change ANYTHING in the design of the mac. Doing a two in one with foldable screen would be minimal at best. SO really there is no design change other than a 180 hinge which is easy, and does not make the device wonky, weird in design or clumsy.