There ain't going to be a Gen 3. Either this is the last x86_64 MacBook Round of updates (2016-17) or in and around 2 years is the last round of MacBook updates. ArmBooks... bank on it. So we will get Gen 2 50% chance x86_64...in 2018-19 (but no Gen 3)...
I think they might phase them in and mix things up, with ArmBooks taking the place of the MacBook (nothing) and then the rMBP getting finalized, then what would be x86_64 Gen 2 of these form factors (Oled Bar etc) and go down to just two Type-C...
And then the whole Mac App Store will be the only way to get apps (ArmApps) on the Machines...
It's going to be a harsh life for some of us...
But fan-less low power fast ArmBooks with iGPUs from the ArmChips is all we're probably going to get...
Being a developer will be great tho, to have Xcode for Arm, on an ArmBook and to run an iOS app natively to test...
Who knows we may even get touch screens on our laptops.
There is only one reason why this might not happen:
If Apple gets a little apprehensive due to the fact that Microsoft had x86_64 and Windows RT for ARM (at the same time) which FAILED Miserably!
But I think Apple is going to go head forward because they are making the chips and going full force dedication to ARM.
If you think about it, if the Mac is going to survive with macOS, it's going to have to make the transition to ARM some time, and Apple has the experience. I would love to see like an Arm Quad Processor "Mac Pro" that would be cool...
But who knows right? (it's all going to be about the SpaceShip Campus and ARM)
I don't think there will be an ARM MacBook because Apple knows it will confuse the product line. Apple likely wants to move beyond the laptop rather than create a new category of it. The iPad is likely to evolve even more to be future of mobile/desktop style computing. Apple is likely to life more successful elements from the Surface Pro.
Multi-tasking is a huge part of the resistance why devices like the iPad are losing the battery against traditional notebooks. Apple will likely make future versions of iOS more desktop friendly. Example, multi-tasking, local file system integrated with iCloud, floating windows. If Apple adds those three basic features, combined with a future A12X Fusion CPU, I don't see what would prevent any user from not wanting to use one.
I don't think mouse support is necessary, I don't even use the touch pad that much on my SP3, scrolling and swiping actually feels more natural. The iPad has that; throw in the smart keyboard with some cool commands and a lot of users would be happy.