You will be addicted until the reality hits you that after that one whole day of walking, running, biking, just to collect the coins, you barely have a dollar. Plus, supposed that the Pokemons can actually be sold for a pretty good price, it will be harder and harder for you to collect Pokemons since the user base will pump up. Another thing, with games like this, the supply is only going up since people can resell their Pokemons and the developer has to spawn more and more Pokemons. The price will eventually go down even when it's supposed to be high.

TL;DR: It can only be profitable at first (assuming that Pokemons have a decent price) but it will eventually be destroyed in a blink of an eye when bot abusers and GPS hackers come in.