Inconceivable they'd do half a job, would make a huge mess of the lineup and would only serve to guarantee developers wouldn't support a fractured ecosystem. That is what I meant with the Touch Bar example, only a few macs use it, so no incentive for developers to put the effort in to make good use of it in their apps.At this point are we really even sure Apple is going to go all in with ARM? They just released their new Mac Pro, I think if they made an announcement of dropping intel in WWDC, that would have a very negative impact on their professional products. I think what's more likely is that they will transition to ARM on some products like the MBA and Mac Mini and leave the "pro" products on intel.
My other thought can really go either way, but its related to developers and Apple's 10% marketshare. Other then getting MS and Adobe to be on board for an ARM based product, other developers may not be willing (or able) to transition over and opt to leave, OR just use their less featured iOS app. For instance, MS office on the Mac is a lot more featured then iOS, yet we could see MS decide to just port the iPad version of Office to ARM macOS. This is of course all speculation, and until Apple formally announces their intent, we are just guessing
I ultimately don't see it making a difference. Just because Macs and Windows are currently both x86 systems, that doesn't automatically confer any compatibility between their apps, they still need to be worked on to be ported to Mac. In the grand scheme of things, if it's worthwhile to port a Windows App to Mac, it's worthwhile regardless of x86 or Arm. If Apple can leverage the massive iOS market/ developer base to get more people buying Macs (maybe cheaper Air models?) that's only going to grow the potential market for Windows-first software.