"Here's some news for the Mac Pro... we plan to ship it sometime next year (hopefully)... oh and it's based on ARM CPUs. In the meantime go and buy our great Intel based systems." Doesn't really sound like damage control, more like adding additional damage.
It seems unlikely Apple is shifting Macs to ARM wholesale. Apple is doing a substantial amount of hand waving when they say the A12X is faster than 92% of the PC laptops out there. I strongly suspect that is based on models sold and not models offered by their top tier peers. All the painfully slow $200-400 based stuff with Celeron and Pentium processors in them that are just "dirt cheap". [ and they might also be sweeping in Chromebooks too although not in the "we outsold them with iPads" numbers. ]
Apple doesn't have viable ARM desktop solution for desktop systems in the > $1K range. They certainly
don't have one for the > $2K range at all. That is just pure arm flapping.
Anandtech did some "breathless" benchmarking of the A12, but quickly tap danced around a real limitation:
"... On iOS, 429.mcf was a problem case as the kernel memory allocator generally refuses to allocate the single large 1.8GB chunk that the program requires (even on the new 4GB iPhones). I’ve modified the benchmark to use only half the amount of arcs, thus roughly reducing the memory footprint to ~1GB. The reduction in runtime has been measured on several platforms and I’ve applied a similar scaling factor to the iOS score – which I estimate to being +-5% accurate. The remaining workloads were manually verified and validated for correct execution. ... "
https://www.anandtech.com/show/13392/the-iphone-xs-xs-max-review-unveiling-the-silicon-secrets/4
The short of it is the A-series can't run an unmodifed SpecMark code.
Apple's A-series are skewed to running iPhone sized jobs. Need to scale to larger memory workloads and it doesn't work as well. The A-series is 'desktop' class as long as drag racing on 32-bit memory space sized workloads. That isn't a viable replacement for the whole Mac desktop workload range. ( yes A-series is 64 bits but that is
far more for better non legacy opcodes and modern instruction set than for memory capacity issues. )
Apple pitching the iPad Pro as a viable "low end" laptop computer range solution does really put much credibility that macs are going ARM. The iPad Pro 12.9" is now the same base price as the non-retina (classic) MBA that Apple has left dangling in the line up. Apple did not move the MBA down in price even though it is a more than fully amortized design. Apple moved out of the MBA 11" price point and never went back down into it. That points as much to "saving the space" for the iPad Pro as anything else.
Apple could tweak the Macbook design so that the list was a bit thicker to accommodate a touchscreen ( and perhaps put a 360 hinge on it ) and just slap a A__X processor in there they'd have an iBook (iOS) based Chromebook like alternative. If the iPad Pro doesn't stop the Chromebook encroachment, they'll have to do something. Lots of folks are spinning "oh, take macOS down market". That probably isn't their strongest move. [ NOTE: Apple's observation that they sell more iPads than Dell/HP/Lenovo/Microsoft combined sell laptops. ( although that was probably not including their chromebook + 'netbook like' options ). ]
A Mac Pro with a 'soon to appear" as ARM primary CPU is largely fantasy hand waving. There is next to nothing Apple is visibly or likely doing that supports that. A Mac Pro with a T-series boot/security/SSD system absolutely. A shipping ARM processor in a Mac Pro embedded in some way is a 'sky is blue' observation (e.g, vast majority of SSD controllers on the market have ARM core(s) in them. Wifi ... ditto. )
The most likely rational for there being no Mac Pro at this point is that Apple hasn't been working on it. No work on the system. No Mac Pro. Nothing to do with new "Area 51" technologies. if they don't do anything, nothing happens. Not having something at this point of 2018 probably means they weren't doing something substantive for a significant chunk of 2017 either.