There is no plan to add subscription for Android for now. Android also charges the same annual fee than Apple and it also takes the same cut per sale, so probably there will be a subscription in the future. The difference is that Apple was selling for half price compared to Android and completely free for more than a month, that's why the subscription was practically a must.
In any case if it comes to subscription, I will announce it way in advance like I did with Apple. Apple players that had paid for the game had been playing for months before they were asked to subscribe (in fact, they are not even forced yet). So it is fair to everyone. New players pay about $1.99 a month on subscription and people that had paid $2 or $4 for the game before, got 1, 2 and even 3 months free subscription on them