Twitter became popular because Firefox / Chrome got rid of their in-navbar subscribe button and Google didn't advertise Reader. They had incentives to monetize doing things their own way, and every average joe who would go to twitter would have the easy path to just using what is in front of them or having to discover feeds in the page info, install an addon to return the subscribe button, and find an RSS application.
Yeah, I think one could have built IRC and RSS into good enough products to essentially reach out to everyone currently using Twitter who never used IRC/RSS.
I still think there's an opportunity for something better-than-Twitter, IRC, RSS in the mobile space. Twitter is SMS mobile, but has what is honestly a shitty client experience on (everything, but especially) mobile.
I wish someone would do something with the same initial goals as Diaspora (self-control, etc.), but focused on mobile, with ease of use on mobile as the goal. Snap Chat is kind of a step in that direction, but I'd rather have something where users got to explore the continuum of ephemeral stuff (like Snap Chat) to semi-permanent (like Twitter) to more permanent (like a blog, designed to be referenced in the future) to really permanent (publishing).
Why are you just targeting "mobile"? If you were making a new global chat system, it would almost certainly be cloud hosted and baked into a web app. The main reason that xmpp / jabber don't catch on is that you can't treat it with delayed delivery like you can twitter, and you can't broadcast messages.
I don't understand how Firefox/Chrome getting rid of their in-navbar subscribe or Google not advertising Reader doesn't just put them at the same level of Twitter when it was just starting out. Twitter didn't necessarily need large marketing efforts to take off as far as I know.
I feel like this is a case of the tech savy being somewhat removed from the majority of the web's consumer base. Honestly, I've had a surprisingly large amount of trouble explaining something like IRC/RSS to someone like my parents or my non-techy friends. I try to explain that IRC is just like any other chat room, but honestly it's incredibly scary and unattractive to most people.