I don't want to rad on your idea, as I see what you're saying but MVP's should be, by their nature, a minimalistic approach to your product which you plan on extending down the road as you gather feedback and validate your ideas through your customers. That being said, when you have a vision of your MVP in your head, as it's minimal you can clearly go in depth with who you want certain parts of the app to work; For instance, if you strip down a lot of features(like you would with an MVP) you're left with a few core features with which you can specifically jot down how you want them to work to the point where you can say(for instance, for upvoting articles) I want it to send an AJAX request, etc. I hope that clarify's the point I'm trying to make.