It's hard to prove it either way, but my suspicion is that there are already more people making their primary living from online comics than there are making their primary living making newspaper comics. And if that isn't true, Patreon will make it true in less than a year from now.

Patreon really is a miracle worker from this sort of niche content. I've seen fairly niche people put up a Patreon campaign, then actually freak out about how much money they end up getting, because you aggregate a couple thousand $1-5/month donations and Holy Shit. (Suddenly it's a Real Job (TM).) It's incredible feasible to go from "scraping by, annoying your parents and friends with what looks like a vow of poverty to do your Stupid Shit and living in constant money stress" to "comfortable middle-class lifestyle with reasonable income assurance". Not perfect, of course, but reasonable.

I mean, look at this: http://www.patreon.com/ZachWeinersmith

Any halfway-well-respected online comic artist not running a Patreon right now needs to get on it.