Thanks for the feedback! The decision for a single-touch approach that prevents moving and shooting at the same time was taken during the gameplay design phase based on two reasons, first one being I did not want to add on-screen game controls... and second one to make my life simpler since this is my first Unity game and I was learning as I went :D
Regarding GWDC I already knew about it and submitted the Android version of the game to the Hobby category, but thanks anyway :)