It has been from day one. Just clone https://github.com/mozilla-b2g/B2G to start!
Telefonica in Brazil is one of the first carriers to distribute it, but I believe unlocked phones will be very common.. plus I've heard you could get an Android device and reflash it with B2G (it's Linux based and should work on the same devices as Android)
I've always been a Windows guy, never cared about free software and such, because it seemed like it was happening without too much fuss, but then, boom. Locked down phones, tablets, etc become the norm. And if our current phones become our future computing devices we are fucked.