Wouldn’t surprise me in the least to have this announced at WWDC, and for the transition to last anywhere between 6 months to a few years, accelerated by App Store binary updates (bitcode or not).
Laptops are most likely to be first, as usual, and an ARM Air would be a thing of beauty, power and grace (now that they’ve fixed the keyboards).
“Big iron” like the Mac Pro, though, is in awkward situation. But Ryzen-powered desktop Macs are not likely to be a thing, regardless of rumors to that effect. Unless, of course, Intel’s deal with Apple is due to expire… But there’s no such thing, right?
So I expect to be running a Linux desktop (with a Mac mini “sidecar”) by this time next year–which is sure to be an interesting journey, especially now that AMD is on the verge of launching new APUs with Vega graphics.
(Life would be so much simpler if there were decent Radeon GPUs out there for ITX cases… I’m willing to start doing hardware reviews of those, if anyone’s interested.)