First it would be good to know whether someone is already working or planning to work here on a native Wikipedia app for Android, with open source license and an aim to become official.
Then I would go for feature parity with the current official Wikipedia app as it runs in Android. I would also follow the look & feel as much as possible except for those cases where the Android native suits better. Maybe the team that maintains the official app has better advice on this.
Last but not least, don't call it "Wikipedia" and don't use the Wikipedia trademarks during the development process. We can sort that out when there is a good candidate to evaluate.
PS: we started drafting a proposal for the process an app has to follow to become official at http://meta.wikimedia.org/wiki/Wikimedia_Apps/proposal . Feedback and edits welcome.