[_underfl0w_]

A better option may simply be to fork and add the additional features, not necessarily create a new client.

[satysin]

This raises an interesting question.

Can one fork the Signal iOS app, add features then publish to the App Store while using Signals infrastructure?

[pseudalopex]

They changed the license so you can publish forks. They're opposed to forks using Signal's infrastructure though.

[saurik]

If you do this you would not get push notifications.