I wouldn't be surprised if Apple cannibalized Mac for that forced App Store and services revenue.
Google is about to dip into that market, where desktop users are forced to use the Play Store to install any app. Apple would be foolish to leave that money on the table.
App instalation isn't really even the problem. It is just the capabilities you have that you do not have access to. a modern iPad can easily run macOS as an 'app', if you will. The kernel is there, the userland is there, just not the checkbox from up high. Even Xcode works well in macOS VMs nowadays.
A fully capable iPad would mean less sales of MacBook Air and so on.
An iPhone with official docking Desktop UI also never going to happen. Same story.