My friend Felipe Baez posted earlier today about an initial High Sierra quick editing test he did.
Using an iPhone 7Plus (only thing he had that shoots in H-265 currently) he shot 4K 30fps footage - brought it into iMovie (X isn't h-265 compatible just yet.) and he says he was able to achieve what he called "buttery smooth" editing on - wait for it - an early 2016 12" MacBook. (NOT Pro, the single port ultra light rig!)
This may get very interesting as all the NLEs gets optimized for these new high efficiency codec workflows.
I can see proxy editing getting insanely more efficient if this trend keeps up.