I think this could be a rather useful addition. I mean I am always using the internet on my phone and of course this needs scrolling and zooming. It could also come in handy for games and apps.
No, the purpose of the crown was because interacting with a tiny screen can be cumbersome in terms of accuracy and not blocking the screen. Can't see using a crown on an iPhone 6 or 6 plus as adding any value.
-Touch screen scrolling works perfectly fine and can be done one handed
-It will snag the edge of your pocket as you try to put it in
-No one likes the protruding camera lense...people will be ready to take lives over a dumb looking knob on the side
- Just one more thing can fail mechanically
-An unnecessary way for water to get inside
- A solution looking for a problem. Would be a total waste of time to design/build this in
There is no practical application for a digital crown on the iPhone. When presenting the Watch they made it very clear that the primary purpose for the digital crown was so you could see the content on the small screen which would have been covered by your finger.
Anything that can be done with the digital crown can be done without it. It's useful, but it isn't needed. It simply lets you see the screen without obstructing it. Putting this on an iPhone would simply be a waste of space.