Re: "Vanishingly Small"
Not many developers use linux in my experience -- as someone who has worked supporting linux-based applications (mainly web stuff) for the past 18 years. I have been primarily linux on my desktop since 1998. I do keep a win7 VM running 24/7 for some work things though.
OS X seems to have killed 98%+ of of the developers I have worked with from using linux over that time. It was sad to see but understandable I guess for their use cases. I don't need more than 1 hand to count the number of folks at organizations I have worked at either developing software that will run on linux, OR support staff that run the linux systems that run linux as their primary desktop over the past decade (I think the actual number may be as high as 3, maybe 4). At the same time probably less than 20 people using Windows to do the same things(guesstimate). OS X dominates.
I tried OS X for a few weeks at one point but it was not my thing. Didn't even like the hardware ended up buying my own laptop so I wouldn't have to use the Mac trackpad (don't like (any)track pads, I want the touchpoint), Linux with Gnome2 + mouse over activation + desktop edge flipping + virtual desktops is what I like the most, so currently run Mint 17 MATE with 16 virtual desktops and the built in display(not a fan of multi display) on a Lenovo P50 laptop.
I was a believer in Linux on the desktop up until maybe 2004-2005, when I accepted that the linux kernel devs will likely never have a stable driver ABI which would of addressed a good chunk of issues with desktops and wide ranges of hardware.
I do use slack on a daily basis(Linux and Android) just for chat at work, never touched any audio or video capabilities it might have. I preferred(past tense) Skype which we were using before, but MS killed that generation of skype years ago and now it's as bad or worse than Slack for chat (don't care about audio/video).
I was die hard irc back in the 90s, the dot com bust caused the communities I was involved with on irc to mostly evaporate and I stopped going. irc is good too though the integrated ability to store messages while the user is not connected is something I never saw in irc (outside of maybe bots or something, I ran eggdrop bots for years).