No, much larger than the issue of open-source is that we already have dozens of major communication protocols that are not based on
open standards or that do
federation (one implies the another).
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.