Go download an OTR client for iOS, like cryptocat and notice how it pings you after 10 minutes that you have to re-open the app to keep on receiving messages! It's because iOS does not allow you to keep an app running in the background indefinately for battery reasons. This is required for the XMPP / OTR model to work.
You need a protocol of some sort that would work properly with mobile, and I think textsecure is it.
I'm trying to introduce the Axolotl ratchet (behind TextSecure's security) into XMPP:
The Axolotl ratchet provides true asynchronicity so you don't need to keep the link open forever. You don't even need the other party to be up; the message can be stored on either server and forwarded when the recipient connects, and the recipient will only decrypt the message at this moment. This is what we need.
XMPP does OTR for example. And you know, the cool thing about an open standard is that it can have many clients. Throw federation in the mix and then many people will actually find it desirable.
Otherwise it's just a matter of being new and shiny. Because other than that, I don't understand how this new messenger competes with Hangouts, Skype, FB's Messenger, WhatsApp, Viber, iMessages, FaceTime, Snapchat, Y! Messenger, Lync, HipChat, Slack, IRC in general, or plain old calls and SMS messages, which are pretty cheap lately in Europe (at least in my country). Note that I enumerated about a dozen of popular alternatives.
I expect new entries to brag about something more than UI. Because my phone has the best UI ever - I just call somebody and that somebody responds because everybody has a phone number. I want to see open standards, federation and encryption, because otherwise new entries are useless for me.
So another proprietary walled garden that promises to keep my conversations secure, cross their hearts? No thanks.