As a case study, I took a real-world app called Text Blast and implemented it side-by-side in both Ionic v1 (source) and React Native (source).
Text Blast allows you to bombard your friends with packs of themed GIF text messages. It strikes a nice functional balance between being simple enough to understand while still being a full-fledged app deployed in production (e.g., not another TODO list demo). And as an added bonus, you get to annoy your friends while testing it out… 
My hope with this side-by-side comparison is that it will help Ionic developers evaluate React Native and vice-versa, since to my knowledge there are no examples of non-trivial open source apps available in both technologies.
I’m a HUGE fan of both Ionic and React Native, and I’ll be posting an article shortly delving deeper into the results of my comparison, but I wanted to post here first to give Ionic devs a preview of the apps and solicit feedback.
Cheers!
– Travis