As much as I love IRC, it is fundamentally incompatible with the way people use IM these days. Even if you gloss over the lack of "modern" features, you're still going to have a very hard time with vanilla IRC on mobile where keeping a persistent background socket open is frowned upon (if not outright illegal).
Don't get me wrong - I love IRC, and have used it as my primary social network for years. And after spending a full decade trying to switch people over to open protocols, I've found the hard way that the network effect trumps all.
I just don't see the average Whatsapp user ever switching to IRC.