I said this very clearly before and was downvoted into oblivion, but I think it needs to be said:

This article advocates for some balance between flat design and skeumorphism. Granted, the article is written decently well, but it does not go into any detailed analysis as to where that balance should lie.

It simply states: Hierarchy should use composition and color. Cool -- basic design principle, check. Beautiful, readable typography? Yes -- sure. Strong emphasis on content, not ornamentation. OK. I've read this 1000x times already. What is new? Where are the analyses or case studies to support the principles?

We need to start talking about where the balance lies and why it lies there. Different interactions will require different balances to find optimality.