If, like rumored, they are switching their pro line to ARM that will impact two groups of big spending customers (i.e. people actually spending many thousands of $ on hardware regularly):
1) Developers buying maxed out pro laptops for running IDEs, Docker, etc. I'm one of those.
2) Creatives using Adobe and other third party tool providers for 3D graphics, movies, photography, etc. This stuff is critical to their workflow and any hint of compatibility or performance issues will cause people in this segment to start considering other platforms or delaying purchasing decisions. I know people that bought the Mac Pro just before it was renewed because they needed it and there wasn't really anything else to buy for them that met their requirements even though it was 3 years out of date by then.
These segments are the ones where switching CPU architecture will hurt the most until such time that the tool ecosystem catches up. E.g. Adobe would have a lot of tools that probably will need quite a bit of work to run smoothly on ARM. It will be interesting to see how long that takes. The last few times Apple switched CPU architecture, it took Adobe a bit of time to switch and it provided an opportunity to MS, which was able to run Adobe's latest and greatest throughout the transition. And emulation is probably not going to be good enough here.
I'm a backend developer and the sole reason I'm still on a Mac is convenience. At this point it's neither the fastest nor the cheapest option. And, I can trivially get everything I use running on Linux or Windows (with the linux subsystem). Most of the stuff I use is OSS, cross platform (IDEs, command line tooling) & dockerized (databases, web servers, search engines, middleware, etc.).
All of that is x86 currently. Theoretically, ARM variants of the stuff I use could be created but in practice, this stuff does not yet exist or is kind of poorly supported/an afterthought at best.
Maybe, emulation of this stuff will be good enough. But still, I'm deploying on x86 and will be likely to want to test on that for the foreseeable future and not run different containers locally than in production. So, my workflow slowing down because of emulation is kind of a big deal for me.
So, (not so) hypothetically if I were to buy a new laptop right now, I'd be looking for something that supports my workflow going forward and that increasingly looks like either using Windows with the Linux subsystem or Linux (Ubuntu is pretty nice these days). Intel macs are still fine of course but not if there's this Apple will drop support in a hurry thing looming over it. I buy laptops with a 4-5 year useful life and Apple losing interest in anything Intel worries me when I'm going to be spending 3-4K on hardware.
The opportunities are also obvious: gaming & VR have so far not happened in the Apple ecosystem and I suspect a big part of the reason is Apple wanting to have their own hardware when they launch this stuff without dependencies on the likes of Intel, AMD, Nvidia, etc.
Also data centers eventually switching to ARM is something that is technically already a bit overdue. At this point most linux software should just compile and run on ARM. Mostly it's just market inertia. Data center supply lines just tend to be dominated by AMD & Intel and developers just happen to run x86 hardware.
So, long term this is definitely a smart move for Apple and I suspect they want to get this over with sooner rather than later. However, they do have their highend users to protect. A mac pro without Intel architecture would be a hard sell in the current market.
Unless of course they really nail high performance X86 emulation. I could see them dedicating a few extra cores to that.