When it happens, it won't be called Linux anymore. It will likely be an OS like Android or iOS with a friendly user interface and a Linux kernel.
Sorry, but most of the user interfaces offered by the various Linux distributions suck. I think that they will continue to suck until the developers realize that the average user is afraid of the command line and are NOT willing to go there to make changes when there is no easy way to make that change from the GUI.
To be fair, many of the recent distros may have fairly uninspired UIs, but they do make it very much possible to never touch the command line if you do not wish to get your hands dirty. Linux Mint and Ubuntu both make it very easy to ignore anything but GUI, unless you want to do something that is not part of the mindset of the developers of those distros. Which is not at all different from any other OS: if you follow their guidelines and/or submit to the will of the developer of said OS, you adapt and make do with what you can. If you wish to try to break free from those rules, you usually can, with some work, or at least you better know how to accomplish some magical feats regardless of the type of interface.
However, I do agree, a modern GNU/Linux distro will not become a runaway desktop hit that even so much as steps on the heels of OS X market share, let alone Windows.
However, take the Linux kernel, fork it (really, give it a good ol' forking, make it forget where it came from!

), and incorporate it into a new OS that, while sharing basic tenets, is really wholly unlike all other variations.
Basically, take Linux and make a new Mac OS X out of it. Darwin is basically a fork of FreeBSD, and that's just the kernel - Apple then heavily develops the heck out of the rest of the OS to make it quite unlike any other *nix OS out there, once you ignore the basic tenets of its ancestry. Which is to say, it still has the X Server (or similar) and Bash and *nix permission scheme and etc etc etc, but using it on a daily basis does not lead to the head-banging that daily desktop use of other *nix systems would be, at least for those who aren't at all familiar with those.
A typical user can jump into OS X with cold feet and, eventually, warm up to it and adapt. Said typical user would probably drown with any other typical *nix distro, regardless of the choice of GUI.
Google is basically taking a Linux fork (I don't think it's the same Android kernel, it could be) and combining that with Chrome to produce ChromeOS. It isn't that much of a stretch to take the modern design tenets of a comfortable user experience, develop a strong developer ecosystem and make it easy to install these apps, remove the barrier of confusing dependency chains, package managers, and repositories, and create a dependable but user-friendly OS.
But there is little motivation to truly do this. Google would be the only one to truly take the next step with ChromeOS and make it a more fully-functional desktop OS. In truth, the only other player even interested in making Linux easier to use is Valve with the SteamOS, which I believe is a Debian/Ubuntu distro that is heavily customized, with the ultimate goal of keeping the user out of the general Gnome GUI, as I think they'll put applications entirely within the Steam UI to accomplish what most users of SteamOS would want to do. That obviously is not the gateway to Linux as a common desktop, that's a very specialized use case, but it does demonstrate the point: a company needs a financial motivation to truly get their very specific Linux or Linux-based OS to become widely adapted. Canonical and the like try with easier-to-use GNU/Linux, but, frankly, I don't believe that approach will ever take the world by storm.
That's why Unix as a whole never went anywhere until Apple and NeXT found a strong purpose with a specific way of doing things (can't remember who truly did it first...). OS X remains entrenched in the creative design world very much due to the core tenets of the platform, no other platform brings printing and color matching to the very front of the operation. The entire desktop management/window server of the OS was always wrapped around PostScript for early print matching requirements, and how they treat color profiles remains the best of all modern OSes, which is actually disappointing.
It's that kind of focus, that type of drive, that will determine whether any other *nix-based OS becomes a hit with any niche outside of the Admin or down-with-proprietary crowds, neither of which can sustain a company to the point that they have the revenue of the major corporations.
RedHat is probably the biggest Linux developer by revenue. They made $1.5 billion in revenue last year, netting $178 million. Canonical, by comparison, brought in $30 million in revenue (no idea regarding income).
[these facts provided by Wiki and Google]
Only groups like Oracle can push *nix to the forefront and bring in serious money, but they, again, have a very specific business and niche to serve.
None of these companies really see a need to get their product to major market share of the desktop, because there isn't much money in it. Microsoft has it dominated and most businesses buy into the model. This is where Microsoft makes their income; consumer computing is an extra bonus, and most simply follow what they use at work because it makes things easy.
GNU/Linux cannot be sold by convention, so a company like Red Hat makes money solely through official support/warranty services. Microsoft, on the other hand, usually gets a double cut: they get the revenue from PC makers who sell a Windows-loaded machine to other companies, and then they get the additional revenue from the CALs needed to utilize those desktops on a business domain, and heck, some more with ongoing support schemes of different structures. Plus they also have the Office suite with the strongest feature set and, due to strength in numbers, is the most compatible. I still cannot stand working with the free Office suites because they cannot render my Microsoft Office files correctly, and Microsoft Office is what the industry has set as standard in the workplace.
Companies simply aren't truly itching for market share of the desktop, other than Apple, and they have a physical product to sell. The OS doesn't even much matter. Because of that, all we will likely ever see is companies like Canonical who care for the niche user groups, those who hate corporations (oh, fancy that, Canonical is a corporation! lulz... yes, not all Linux distros are backed by corporations, but Debian sure as hell ain't gunning for the casual user), hate proprietary standards, or simply like to demonstrate their 1337ness and use the stuff that most users look at and run away scared, or at least force eyes to glaze over.
I think it really is only a company like Google that could make it happen, because they have a financial incentive to take over the casual user's lives: more advertising dollars, as the casual users will just take the product and run, not digging into privacy settings. I use Google products, but I don't use them when I care to hide anything from the world, so I don't care much. The convenience and free services are worth it, it is an acknowledged price for said free services. Google could very well make it happen to further their reach and increase both user data prices and ad prices due to increased advertising reach.
Which all of a sudden really brings me back to the whole "do no evil" thing. They may truly do no evil, depending on who you ask (certainly not the privacy advocate groups!), but they may very well become the corporate big brother who basically oversees our lives like various sci-fi stories have promised. They'll have the data and also be everywhere and, as a consequence of wanting to increase revenues (thanks, shareholders!), they'll have motive to penetrate
us our lives more than ever.
uhh.. holy wall of text batman. D: I'll quit there. :biggrin: