Let me start by saying that I really like this idea.

Obviously social apps like this are faced with a chicken-and-egg dilemma of how to acquire users. I'm no marketer, so I don't have any suggestions on how to solve this one.

For myself, I avoid non-free/open-source programs in general, but especially chat apps. I think that especially the programs we rely on to communicate should at least be transparent on the client-side. That being said, I would absolutely try this out if the app were released as FOSS (which it doesn't look like it is?).