It's certainly normal for smart device apps to be updated frequently, and Miitomo is no different. It's already up to version 1.0.2 in Japan as Nintendo and DeNA have fixed some early issues in the app.
What does seem to be on the way is a more detailed update to add new features, providing early delivery on the promise that the social app will continue to evolve following its launch. Well-known gamer and resident in Japan 'Cheesemeister' has been posting fairly regularly about Miitomo, and has shared an image showing that a new update will add additional friend options along with more ways to view and share "answers".
We trust that - assuming there are no logistical issues - the Western version of the app will be fully up to date when it launches; whether this update will beat the global roll-out to the punch is unclear.
In any case, we're intrigued to see how Miitomo can make an event out of answering questions.
Thanks to all that sent this in.