But, I've been in a primarily OS X desktop environment and primarily Linux server environment for close to the last 10 years now. With that experience, here are some places where I believe Windows is still deficient, and will remain deficient as a development environment that works for the majority of development languages (not just Windows-based) for at least a few years, possibly much longer.
OS X embraces Linux/*nix as far as command-line tools go via Homebrew and has maintained a reasonably active community with that. Windows has Chocolatey but that's not a replacement for all of the tools, and at time of writing Scoop is also really lightweight compared to the long list of formulas in Homebrew.
Sure, OS X includes bash at command-line, and yes, Windows 10 will provide it and support for other commands provided in Ubuntu to work by using an adapter as part of Windows.
However, that doesn't go far enough.
In order to be an easy-to-use Desktop environment, a powerful development workstation, and similar enough in the underpinnings to be fairly compatible with the most stable and ubiquitous server operating systems which use the Linux kernel, Windows would need to be a Desktop manager atop Linux. That won't happen anytime soon, and is not in Microsoft's plans.
Why does it matter? I've personally seen the pain of a developers trying to migrate to Windows from an environment that was targetted at Linux, in languages that for the most part assume to be run on Linux servers, and with developers that use OS X or Linux... and it is painful. Incompatibilities galore when you swim against the stream. And, no developer should be put into this situation. If the money is there, the right tools should be used for the job. This may mean that your best environment should be composed of teams running Windows, OS X, Linux, and more. While there is something to be said for developers using the same tools so that they can work with each other more easily, you shouldn't ever continually force developers to use the wrong tools for the job or switch to them unless you want them to fail.
I really want Windows to provide some serious competition to OS X and Linux in the realm of all types of development, not just .Net and the like. If it could be better than OS X for all developers, I'd use it. But, even if I start buying Windows PCs at home here and there now that Windows 8 has mostly run its course, I can tell you that I don't see a future in the next few years where I would enjoy writing code in Windows, unless I'm writing code in .Net or other languages where Windows might be a better choice.
That said, Windows still has the majority share in Desktop operating systems, at time of writing. 46.66% Windows 7, 13.65% Windows 10, 11.67% Windows 8.1 vs. 9.03% OS X according to StatCounter for January 2016.
But, in comparison, public servers on the Internet are 35.9% Linux and 32.3% Windows. For the most part, I develop software that is either run on or is served by similar servers, therefore it continues to be in my best interest as a developer to develop in an OS that not only has a terminal with a bash/zsh shell, but works more closely to Linux where I can use tools in the terminal that work similar to those that work on the servers that the code I write will be run on.