Will depend on the OS. The MacBook Pros have had this for some time and MacOS will use the dedicated GPU in certain situations. Depends on many factors - what the application requires, is the computer plugged in, how much battery life is available... Apple has more control of software and hardware so implementing this sort of solution is easier for them. I've heard some complaints but not too many. Do not know how Windows manages this. And Linux? Without capable hardware in the hands of developers one can not expect much progress. And considering the perpetual state of video drivers on Linux.....
But as far as the hardware goes, the integrated GPU is going to be available even if when the external GPU is present. It is likely Dell uses the same motherboard for both laptops - they just neglect to install the external GPU in certain models. This is how manufacturers typically approach this problem.
Backwards compatibility is worth more then extra battery life. The A series CPUs are excellent and I am certain they cost Apple less then the Intel chips but adopting them for current products would cause too much grief. Intel is still improving their CPUs and not forcing Apple to switch architectures.
For new platforms, the A series CPUs are an obvious choice. I could see a version of MacOSX being ported to the latest large iPads. In time, the software ecosystem would develop to support the ARM CPUs and eventually, an ARM laptop could be viable. But this would take some time and would require Intel to drop the ball. I do not personally see it happening anytime soon.
If you want per-application snapshots then you want the application to be in charge of the snapshots - not the file system. The file system does not know when an application is finished making changes to a file. Possibly many files must be changed - the file system does not know so it can not make any assumptions. Applications should be in charge of their own document snapshots using some form of version control. If one wanted they should script it so that a ZFS snapshot was generated - but you are better of using git.
With regards to ZFS, the snapshots are generally done at whatever frequency is defined by the administrator. 5min, 30min, 1day - whatever they decide. The snapshots are accessed from the root ".zfs/snapshots/named_snapshot" directory. There is no piecing together of files - the full file-system, as it was at the point in time it was captured, is available in the directory. The snapshots are immutable - the contents will never change so long as the snapshot exists.
It is more likely that Apple designed USB-C at the same time they designed the Lightning connector. They opted for the Lightning connector and decided to gift USB-C. It is in Apple's best interest for USB to have a good connector.
Looking at how horrible the USB3 connectors are, it all makes sense. USB 3.1 was announced far to quickly for it to have been planned at the time USB 3.0 was being specified. And there was no design debate - the new connector was basically just announced. Looks like someone delivered a fully developed USB-C connector to the USB standard committee and it was enough of an improvement to warrant a new version.
"I never let my schooling get in the way of my education." -- Mark Twain