Comment 1 for bug 1625365

All in all, your points make sense, but we've a bit different solutions in mind:
- you will be able to change the behaviour of every screen separately, in the same area you'll be able to change screen resolutions etc. - that's where you'd choose a screen to go into desktop mode
- the "mouse pointer" function will become an app that you can launch on the phone while connected to an external screen - but you won't have to.
- rotation of the phone screen does not affect the external screen (unless they'd be cloned, but see next point why it would be better not to), and the rotation lock you would configure in the same place where you set resolutions and usage modes
- whatever presentation app you use could provide a "remote control" window that would be displayed on your phone - think of the LibreOffice extension "presenter console"