Fomr an Avaya standpoint, there are some features that AVaya has now brought into ACO, that can only work on J series phones, and only ACO, not RCO. Avaya sells ACO with Avaya Logos and Avaya development. So now you get Avaya and Ring development on a platform that will move PBX features to RC, and only available from ACO/Avaya...

Mitels was an interesting deal. Mitel sold their Cloud/prem server intellectual property/patents. Mitels offering will just to sell RC, so there is no diofference.