A few months ago I saw the proposed 2015 DPS road map that had been circulating around. On that road map there was a feature called "search".
Are you able to let us know what your "search" term might consist of? Searching just inside certain articles? or a would this be a much wider search through-out the entire app experience... im assuming that is why you have chosen to add all the meta-data fields etc.
Another question we are wondering about is whether or not you will allow articles/content to be indexed with search engines?
In-app search to discover content. This would be an interface that returns content based on a query. Articles, collections, and potentially other content elements would be returned. Your assumptions about tagging content with metadata is correct, we will definitely utilize it in search.
Find a word in an article, navigate the user to instances of that word in the article. That's the first use case you questioned.
Search Engine Optimization, allowing content to be indexed more broadly.