What I'm worried about with retina displays on Linux
I've been waiting for high-DPI LCD panels to appear for years, so I'm both happy and excited to see 'retina' displays start to appear on desktop machines. Recent announcements even put a usable such panel within theoretical reach. But this means that I have to start worrying about one of the problems I may have with them, namely whether or not I'll be able to drive such a high-resolution panel under Linux.
Mac and Windows people don't really have any worries here. Since these panels are useless without the ability to drive them, there's going to be graphics cards that can do the job. By the time the market drives the panel prices down to less stratospheric levels, these cards should even be fairly widely available (although they may well still be relatively high end cards).
But I use Linux and I go further than that by insisting on using open source graphics drivers. The open source drivers almost always lag behind in both hardware support and feature support, while driving really high resolutions is likely to be a leading edge feature for quite a while. I can thus easily imagine a future where the only cards that can drive the high-DPI displays I want are high end ones that aren't supported in open source drivers and won't be for years to come.
(In fact the hardware that's best supported in open source drivers today seems to be Intel's, and who knows if Intel will even make a graphics chipset that can drive big high-DPI displays. So far all Intel chipsets have been integrated into motherboards, and people who buy systems with integrated graphics are often not seen as people with demanding graphics needs.)
By the way, there are of course a lot of software issues that are going to come up with really high DPI displays on Linux; many things work in absolute pixels (which are going to be tiny) and many graphics and icons won't be available large and won't scale up. I'm sure I'll be looking various tiny little pictures for years. But I also expect that all of those issues will get solved relatively fast, partly because they're also an issue on laptops with high-DPI displays.
(I suspect that some of them have already been solved in some desktop environments.)
PS: The current lot of 4K TVs are not useful for me as displays because they have too low a refresh rate. I've historically been quite sensitive to this issue with early LCD panels, so I'm basically sure that 30 Hz is not enough for my usage. Future 4K TV panels will probably improve that, but I'm holding out for high-DPI 5K displays since they've started to show up too.