You do have Java expertise, so Android would be a logical step. Try out Jetbrain's and Google's new Android Studio to leapfrog over the Eclipse experience. Alt

You do have Java expertise, so Android would be a logical step. Try out Jetbrain's and Google's new Android Studio to leapfrog over the Eclipse experience. Alternatively learn AngularJS or a similar JS framework and use PHP to serve JSON to state-of-the-art single-page type apps. You can run such PHP scripts on the new Appengine for PHP, so you end up with a highly scalable solution that is also not bad in performance. I think the best way to progress is take something that you know and combine it with state-of-the-art practises or tech. Be glad that you didn't learn some of the technologies that developed over the past years (Rails for example is starting to get out of fashion since it is not so useful/overkill for JS apps) and leapfrog to the new ones.