If we go to a model where people pay $1.99 and say get the first month free, they would still have to sign up for the IAP sub to continue. The other issue is it would allow pirates to download the game and play for a month for free, since there is no real mechanic to see if you actually purchased the game.
Having the IAP subscription model from the start it allows us to have everything set up and running from the start and not have any issues with pirates. We have thought about having IAP where you can buy credits to play in a game, but that certainly won't be at the start.