The Idea:

A Steem "App Store" would revolutionize the free app model for developers.
This store would function much like steemit, except instead of using votes, it would use downloads and reviews.

High downloads + good reviews = more money.

Reviews should of course be weighed far more than downloads, as to prevent low quality "click-bate" apps from rising to the top.

This model would effectively kill off both microtransactions AND advertisements. Both of which hinder the user experience, and generally make aps worse!

Implementation

The appstore could be a subdivision of the upcoming Steem Market.
It should also allow users to create "premium" apps, in which they can charge Steem Dollars for.

Conclusion

I think this would be a fantastic way for devs to release high-quality work, reach their audience, and still earn money for themselves WITHOUT hindering user experience. Let me know what you guys think.