My point was not that we don't have choice today (we do), it's that we're not going to have choice in the not-so-distant future as these other OSes die off (incluing Firefox OS).
Sure, you can root some Android devices and install Android ROMS like Cyanogen... but those are just Android. We're going to lose the creativity we're currently seeing in Jolla, Windows Phone, Firefox OS, Blackberry, etc.
Can I buy any phone, and then wipe it out and add any OS on it?
I think that is what the OP was driving at. And that would be quite something, compared to current state of affairs! :)