* Hiri went to Reddit. I would think that the r/linux community is a very tiny subset of users. Young and bored, who just want to be part of something? Criticizing the mainstream like Microsoft, Ubuntu, GNOME. Like goths and punks from before? That was the impression it gave me when I visited it a few months ago. Doesn't seem to be very representative of the average desktop Linux user.
* IRC is likely too technical. Finding sysadmins and developers there should be no problem, but they're likely not your average user.
* Since Linux is such a small section of the market, it probably won't be of any use to try other social media websites. You can find Windows and iOS users in any community, but not Linux users.
Unless there is no such thing as an average Linux desktop user. Maybe there is no mom & pop, without geeky interests, careers outside of tech, who have Ubuntu on their laptop. Maybe it's all sysadmins, developers, nerds, and youngsters. In which case I don't think there will be a lot of reason to sell anything there other than games and tools like Sublime, although the games might be better on Windows and iOS.