I think Apple will do three things:
1. Introduce non-retina mini with A6 starting at $299.
2. Introduce retina mini with A7X starting at $399.
3. Introduce iPad 5 with Touch ID and A7X for $499.
The retina iPad mini will not replace the current mini. I learnt my lesson with the 5C, Apple does NOT do cheap.
You gotta great point... That will keep their price margin at a great state with your three points. So, Apple will discontinue the last generation iPad Mini and iPad 2. Cause I know they will do a price increase on a retina iPad Mini... It's still going to sell like hot cakes.