Fair enough. I'm not a Mac OS X user so I don't know how it would compare. I can only compare it with my past experience with Windows, and I think it's superior (for me) to Windows circa 7 -- I stopped using Windows entirely at that point, so I wouldn't know how later versions of Windows fare.
Portability is also a fair issue to raise, but it's simply not a problem for me. When I say Linux "on the desktop", I literally mean it: to me a laptop is simply a slightly more portable desktop computer. I sometimes take my work laptop to/from the office, and the battery lasts long enough for that. I'm not worried about longer trips, since I don't use laptops for that. Again, if you do care about this (which is completely fair), I'm aware many Linux distros still have issues with battery life. You certainly can't compete with a Macbook Pro, that's for sure!
I do note that my experience with printers is opposite to yours. Like I said, when trying to connect to an HP wireless printer, Ubuntu autodetected and self-downloaded the necessary drivers; however, it took a lot of patience to get it to work with a Macbook Pro. Today, that I have it configured for my Ubuntu laptop and my wife's Macbook Pro, the Mac will sometimes fail to print (the print job simply stuck in limbo) while my laptop prints reliably. Who knows?
And like I said in another comment, I game (or used to, anyway) a lot with Ubuntu, and many games are even AAA (though they tend to arrive later than on Windows).
So I really have a hard time believing Linux is not "ready for the desktop". It is, and has been for many years now.
edit: one last thing. You mentioned HDPi modes, multimonitor, multilanguage... none of those are for average users. My mom would be comfortable browsing the net, reading mail and watching movies on Ubuntu. She doesn't even know what HDPi is, nor does she want external monitors. (Spoiler: she still uses Windows because she can't learn anything else at this point... I've thought of tricking her by themeing Ubuntu to look like Windows, but that would just be mean).
Without HiDPI support lots of applications become useless when you use a HiDPI display. Even Steam does not respect HiDPI settings in Gnome 3 even when setting custom environment variables.
It's probably a case of "I don't miss what I don't use" then. I'm a power user, I cut my teeth with MS-DOS and I've been using Linux for work and gaming for more than a decade (and less intensive usage before that) and I really never noticed anything about HiDPI. That has to mean something :)
For the printers, you are right in that it’s far from being a solved problem on macos. I had an EPSON all in one before, and it was also a pain to get everything working. If I remember correctly the generic driver could print, but we didn’t get “advanced” options without going through the EPSON pkg installer and all the garbage coming with it. I’d totally imagine the linux driver being done cleaner than that.
For the record I’ve worked with a decent number of devs using linux workstations, so I totally vouch for your use case. I’d just temper the niche nature of multi-language support; that’s an everyday need for basically all Asia. Granted my use of shortcuts is niche (I wouldn’t need them if I had enough keys), but looking at maintenance projects annual reports there seem to be a sizeable amount of quality of life fixes still on the way.
Portability is also a fair issue to raise, but it's simply not a problem for me. When I say Linux "on the desktop", I literally mean it: to me a laptop is simply a slightly more portable desktop computer. I sometimes take my work laptop to/from the office, and the battery lasts long enough for that. I'm not worried about longer trips, since I don't use laptops for that. Again, if you do care about this (which is completely fair), I'm aware many Linux distros still have issues with battery life. You certainly can't compete with a Macbook Pro, that's for sure!
I do note that my experience with printers is opposite to yours. Like I said, when trying to connect to an HP wireless printer, Ubuntu autodetected and self-downloaded the necessary drivers; however, it took a lot of patience to get it to work with a Macbook Pro. Today, that I have it configured for my Ubuntu laptop and my wife's Macbook Pro, the Mac will sometimes fail to print (the print job simply stuck in limbo) while my laptop prints reliably. Who knows?
And like I said in another comment, I game (or used to, anyway) a lot with Ubuntu, and many games are even AAA (though they tend to arrive later than on Windows).
So I really have a hard time believing Linux is not "ready for the desktop". It is, and has been for many years now.
edit: one last thing. You mentioned HDPi modes, multimonitor, multilanguage... none of those are for average users. My mom would be comfortable browsing the net, reading mail and watching movies on Ubuntu. She doesn't even know what HDPi is, nor does she want external monitors. (Spoiler: she still uses Windows because she can't learn anything else at this point... I've thought of tricking her by themeing Ubuntu to look like Windows, but that would just be mean).