Because of Apples experience custom designing ARM processors for the iPhone, iPad, Apple TV, etc. — by far their biggest selling products — it is a natural fit and would enable Apple to optimize performance and features for MacOS as well as iOS/iPadOS.
You followed that with some thoughts about the advantages for iPad and then "Maybe not this year". As a birthday present, my wife has suggested it's time to replace my old MD520C/A iPad but, as I am a person who keeps stuff for a long time, would I bump into problems if ARM processors migrate to iPads two years out? The fact that I cannot any longer move to newer iOS's on the MD520 doesn't bother me as I don't do anything confidential on the iPad.
