This feature is a show-stopper level requirement for using Mattermost on Mobile with companies in the Microsoft/Azure ecosystem.

Reason being that most large scale companies have centralized identity management and have policies that prevent any application into their ecosystem if they cannot centrally control access to it. As an example, corporate IT usually want to make 100% sure that when they disable a user account from their AD, the change is carried over to all business applications and there's no risk of the user retaining access to company information once they have left. Using a central identity provider also makes it possible to force sufficient level of password compliance, multi-factor authentication etc.

Because ChatOps is mainly happening on the go and in real time, selective push notifications on mobile are a must feature for adopting a chat app.

As Mattermost native mobile apps now don't have support for Office365 authentication, you are effectively preventing many of the enterprise grade companies in the Microsoft ecosystem of adopting Mattermost in any large-scale way.