So, it is uncertain whether it will ever be the case that the majority of devs use Linux although I guess there's a good chance of it happening if Apple ever decides to abandon the desktop / laptop market.
There are a lot of great things about linux and some of the desktops are quite good (gnome 3.4+, kde) but they just aren't quite there with the small glitches and annoyances that come up just often enough to be off putting for end users.
I think linux or another free OS needs a huge backing to make it mainstream and we may see that with android (or something in a similar vein) in the future but for now the desktop is left Apple and Microsoft
Don't work on open source, unless you do everything each person wants (and these may be conflicting) then someone will decide it isn't open enough regardless of the actual license.
With proprietary OSes I constantly have the feeling of banging against elaborately engineered limitations. This feels so counter-productive. Instead of producing something great why not spend incredible amounts of work-years on creating artificial limitations for the users, right. No thanks.
In other words I like my computers to be general: https://www.youtube.com/watch?v=HUEvRyemKSg
Anytime someone comes up with an extremely good app.. It magically becomes part of iOS leaving that person high and dry. Done. With. That. Shit.