Apple switching to Arm would be near impossible given many people run windows on apple and other non-apple programs that won't be able to be emulated fast enough on Arm. Steve Jobs might try that leap but Tim Cook won't want to scare anyone off from the Apple ecosystem.
IIRC it was there in betas for a while. Typically when a feature was pulled from OS X betas it was either because it was too broken to make the release date, or patents.
1. The expected plan was to transition the MacBooks across first. Those users were never able to run Windows properly anyway and their apps aren't likely to be CPU bound.
2. The idea isn't to emulate OSX apps. It's to repurpose them to run on ARM. And they been doing this with all of the App Store apps for years:
