Distribute Office 2016 apps via the Mac App Store
Receiving updates would be easier avoiding the malfunctions of the AutoUpdate app.
Also, there is no requirement to provide the service subscription within the app. Just the ability to sign into existing accounts for Office 365, on-premise exchange, gmail, iCloud, hotmail, etc. This is already the case. Users cannot subscribe to Office 365 in app on the Mac apps.
The royalty conversation is a cop out. Apple has already demonstrated that they will negotiate with large partners on different terms as well as eased up on the subscription fees.
Regarding the 30% royalties, I know that but Microsoft could make a basic version of the apps free to download and access to the full version for those who have a license purchased from MS website (same as iOS apps but without the buy-in-app option), and limiting in this way the number of functioning full version to the number allowed by one's own license.
Regarding the restrictions Apple puts on developers, I admit I don't have a wide knowledge about that but I understand it is hard to do.
The problem here, is that Apple takes 30% off the top.
I agree it would be awesome and much better for the end user, but If Microsoft were to do this, they would have to charge 30% more to make the same amount. (I would actually consider 30% more since you can use it on several mac's (up to 5) so it would be worth it... but thats another thing Microsoft does not like, they do 1 or 3 machine licenses, unless you subscribe to 365 etc...
Not only that, but there are severe restrictions Apple puts on developers that use the store, Like what system files the apps have access too, how it connects to the net etc... they may have to remove many features to comply with this. Features such as the apps talking to each other, like one drive integration, or shared spell checkers etc...