Should the central server be the only missing component of a reliable, secure-paranoid, mobile IM system, I would be happy donating some dollars.
The general idea is that you'd fetch tokens from the server that allow people to send pushes to you, then distribute them to trusted contacts over an secure channel. Contacts would then be able to send you pushes from any endpoint of choice. Somewhat less metadata than existing solutions, and an opportunity for client diversity.
p.s. So honest is this app to explicitly state that I need to keep it foreground to receive new message from XMPP server.
They also have attitude of "oh we are smart, you just don't get it", which is not the way anyone should think about cryptography.