I strongly believe the challenge for the Mac is not in the Intel vs ARM part, but on the iOS vs MacOS part. And this is not because of OS design choices, but because Apple has decided to be mostly a services/subscriptions business, and the success of this kind of business greatly depends on not letting the user be in total control of their devices, just like all mobile-based OSs do, iOS included.
In the past, Apple was a product-based company, where the user got a product as a final purchase rather than as a subscription, and thus it made sense to have a very powerful OS in which the user had total control of everything. NeXTSTEP was a perfect choice for this.
So, answering to the OP thread question, I don't believe ARM will introduce great changes in the paradigm, but I do believe that, no matter if they use Intel or ARM, they'll decrease the degree of user control in MacOS, so that it behaves more and more closer to iOS, where Apple has the control of what the user can choose to do or not.
Therefore, in conclusion, we have tough times for the Mac in the horizon. This can spread to other non-Apple computers as well (and it already started: non-user avoidable updates in Windows 10, for example). And, in the end, this could mean that computers might go back to being expensive, just like they used to be in the past (I mean, if all the people needs are going to be done with mobile OSs, mobile devices will be cheap, while computers will be expensive if very few of them are sold).
It seems we have bad times ahead for computers.