I’d try to keep everything in the same app so you can share the same singletons and caches, etc, and swap out handlers, views, and layouts where necessary. If you can make responsive views, you may be able to re-use as much as possible and let CSS take up the slack. Take my ideas with a grain of salt though as I have never really implemented a full mobile solutions, so this is more what I’d try, not what I’ve actually done 
Thanks!
~Brad
ColdBox Platform Evangelist
Ortus Solutions, Corp
E-mail: brad@coldbox.org
ColdBox Platform: http://www.coldbox.org
Blog: http://www.codersrevolution.com