Since 1980 ANH has been Episode IV.

As I said I have some sympathy for people who say the films should be watched in the order they were made but there is no reason why the plot of the films shouldn't work in either order.

If you don't know Anakin is Luke's father when you watch the prequels it should maintain the surprise of ESB and the audience still sees Vader become a cyborg they just don't know he is the father of the protagonist of the next three films yet. Giving Obi-Wan a prior pupil is one way of making that happen.

To be honest the birth of Vader in ROTS is so badly handled I'm not sure if any of the material is usable but I wouldn't 'kill the idea' of using it. Someone might be able to get it to work.