One incentive would be stealing customers, and removing one last excuse not to get a mac.
As a hackintoshers, I desperately want Apple and Microsoft to make this happen. I'm at a point in my life where I'd happily dole out the money for a rock-solid mac studio given the major performance boost over the intel hardware, if it could run Windows and interface with a discrete GPU (if necessary).
I'm ready to repent and give up my hackintosh-ing ways because I don't have the time to keep up, but at the same time I don't want to manage two different computers—I can't use two at the same time, and I'd rather all the money I pour into one system for beefy specs to be reused for my semi-regular/sometimes-occasional gaming.
How many more of me exist? I don't know, so I don't know if that's a big enough slice of the pie that Apple is interested in claiming. I wonder how many other folks like me exist but who haven't been indoctrinated in the Apple Ecosystem and might convert over given the exposure/opportunity.
If ARM architecture really is as gangbusters and amazing as the frenzy surrounding it seems to be, it feels somewhat innevitable that consumer tech makes a full transition. That being said, folks earlier in the thread have made some good points about how long (and incomplete for that matter) other transitions have taken, like 32-bit to 64-bit, which really pales in comparison to a full architecture change.
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