Plus, competition in the form of other closed source products, or even those with more liberal licensing (such as the various BSDs), hasn't really materialized to the degree that Linux runs the risk of being pushed aside.
Sammer sums up the biggest legitimate threat to Linux in a single word: complacency -- the complacency that goes with becoming a market leader in any field.
"If you're vying for first place," he says, "you're usually more open to change of process, of mindset, of road map, of status quo, whatever. I can't help but think of Firefox losing so much to Chrome so fast, or the commercial Unixes losing to Linux, or all the other examples of such things."
In roughly the same vein, Zemlin sees a threat in the form of a lack of experienced Linux talent to support the demand; hence the Linux Training program.
Gillen sees a threat coming from a transition that "over time, moves the majority of the Linux user community from the enterprise customer over to service providers."
Such a move would put Linux users at the mercy of people who may consume Linux and provide it as a service but don't return their innovations to the community as a whole. It may take a decade or more for such a shift to happen, but it could have "negative implications for Linux overall, and to commercial vendors that sell Linux-based solutions."
Another possible threat to Linux is corporate co-opting -- not of the code itself, but of the possibilities it provides. Baker is worried about the rise of mobile devices, many of which, although powered by Linux, are powered all the more by corporate concerns.
Of those two, Google -- by way of Android -- is the main offender in this accusation. Many of the arguments against Android revolve around it being a Linux-powered OS that's little more than a portal to Google's view of the world, and thus isn't true to the spirit of Linux.
In short, the biggest threats to Linux may well be from within -- unintended by-products of the very things that make it most attractive in the first place. Its inherent mutability and malleability has so far given it an advantage over complacency and co-opting, but it isn't clear that will always be true.
Where from here?
Linux is unquestionably here to stay, and in more than one form. But how it will do that and at what cost are up for debate.
The most obvious future path for Linux is where it becomes that much more of a substrate for other things -- a way to create infrastructure -- and where it becomes that much less a product unto itself in any form. The real innovation doesn't just come from deploying Linux, but deploying it as a way to find creative solutions to problems, by delivering it in such a way that few people are forced to deal with Linux as such, and by staying a step ahead of having it put behind technological bars.
Coggin puts it this way: "Linux is emerging beyond that of a packaged or flexible operating system to become more of an infrastructure platform. With this, we see developers and architects using Linux to build next-generation solutions, and creating next-generation enterprise architectures." Much of this work is already under way, he claims, in "cloud, big data, mobile, and social networks."