Visual Studio is actually an awesome development platform (I’m including VSTS in this). There’s not much secret sauce in Xcode to threaten Apple’s App Store revenue — it’s just a bunch of signing keys that Apple controls and manages.
I do think Apple will make a strategic decision to diversify from core Mac OS soon. The ever-shrinking space allocated to traditional computers at the Apple Store has convinced me of that. They have more floor space allocated to the Apple Watch than they do the Mac these days.
And honestly, their desktop line looks very similar to many PC companies. They make the Mac Mini (aka the Apple NUC), the all-in-one iMac, and the Mac Pro (ok, the Mac Pro sucks and there’s no excuse for it).
Anyone doing serious workstation tasks these days is likely using a cloud-based solution. There are a few specialized exceptions (ML development stands out to me), but none big enough to build a product around. Especially when doubling the entire PCs and Laptops category wouldn’t move the needle for Apple at all.