Imagine a mobile text chat app that's a cross between Delta.Chat and Silence (defunct SMS app forked from early Signal);
https://f-droid.org/en/packages/org.smssecure.smssecure/
As well as being the mobile app for my personal email address, it could also replace my SMS app. With the capacity for E2EE text when the other person's app supports either AutoCrypt (or something based on the variant of Signal's protocol that Silence uses).