That's assuming users choose the Mac instead of PC.
The iPad is pretty much the de facto choice for tablets. For desktop-only stuff, I'm more than fine sticking to inexpensive Windows PCs since I only use them once in a blue moon (outside of work that is). Both Mac and Windows will run Calibre just fine and DRM removal software (e.g. Blu-ray ripping, etc) are often Windows first.
For Apple, the goal will be iPad Pro vs something like Microsoft Surface and other Windows convertibles. Looking at it from a broader perspective, it's in Apple's best interest to expand the iPad Pro's capabilities.
I think Apple does not see it this way... An hybrid would not move many Windows users to Apple, not much more than ipad does now. Those of us who use Windows don't need an ipad to have touch, pen and even silent operation (surface pro i5 if fanless, as is surface book 13.5 up to i7). But we still have ipads as companion devices because of portability (and I am not talking of the heavy magic keyboard, but he simple smart keyboard), choice of sizes, speakers, cellular together with some great IOS apps. Surface is no threat to Apple. For Apple fans because of software (they generally hate Windows), for Windows people like me because of hardware (lack of decent speakers, bezels, partial lack of cellular, and problematic CPU for the price for the only surface that has all this, the pro x, which by the way comes only in 1 size).
Some form of Apple hybrid (like an ipad with macOS or a convertible Mac) would mainly cannibalize other Apple products and would go against the very idea of ecosystem that Apple has been building (buy as many products as possible that all work together, iphones, ipads, macs, airpods, watches, tv and other home devices and all the accessories....) so it would be more harm than good to Apple despite how desirable it would be to some of their clients... (I mean this very thread is about some people already thinking of giving up ipad pros for the latest macs, which are revolutionary in terms of power and efficiency, but have quite poor versatility, since they are just laptops, no touch, no pen, no cellular, no under 1kg devices, at least for now...)