Hopefully, we would be OK with regard to securities law if we premine 100% and distribute those coins to users of our app at no cost.
I think so if you can also get many other apps to use your coins and create a huge diverse ecosystem for these tokens (but I don't think you can do that without losing your focus on your app!), but consult your own attorney. Note smooth and others felt premine was culpable. I argued against that. None of us are lawyers.
I doubt distributing 100% at no cost is a problem.
What I suspect will never escape some degree of capability is selling ICO coins. No matter how many times and how many different ways you claim "it isn't an investment" we all know it really is an investment. Prosecutors and judges know too.
But sure get your own legal advice. Better yet, pay multiple lawyers to give you different advice. Then you can pull out whichever one you need and claim good faith since you were relying on competent advice of counsel.