Macipad is the future
The future of Apple is a world of Macipads. Looks like Macs, works like an iPad. Great for data consumption and specific narrow applications. It'll work for 90% of the consumer workloads, but anyone trying to do some heavy lifting will be SOL. And kiss your existing software investment good bye.
And it's not just the software. Imagine all the hardware that will be paper weights without new drivers. The narrow set of providers for Macs will become even narrower, with the "high quality" drivers from the usual suspects being even "higher quality" on a new platform. Even today it's a Mission Impossible trying to get a decent scanner with software that works as well on Macs as it does on Windows; I presume in the future with ARMs it'll be even more so.
This change is Apple effectively forcing its users to go on a beta-journey for half a decade or longer, while they debug the OS, the processors, the ecosystem, and then slowly supporting vendors do the same. It does not sound very inviting to me.