It looks like you're new here. If you want to get involved, click one of these buttons!
Well not really one payment model, but three designed to work in tandem in the same game, all the while avoiding the pay to win issue and allowing as many people in as possible. I could smash this thread with an essay but I'll let the proposed systems talk for themselves.
Everything is given to the player for the usual price, £9 or 12 euros or 15$. They do not have anything to purchase to unlock in terms of features, areas, classes or races, inventory slots, character slots.
Build your own subscription.
If you cannot afford the subscription costs, then perhaps the build your own subscription would work out better for you. Perhaps you only intent to play a certain amount each day, or maybe you only want four race slots and half of the classes on offer. This is a more advanced option, but the player would be able to add things until they were happy, or until they finally arrived at a point where a subscription was a better deal.
Free to play.
The free to play option would allow the player access to the game, a selection of races and classes, limited race slots, limited bag slots, limited coin allowance. Then you let the players pick what they want to buy outright, perhaps they KNOW they never want to touch a caster, and are SET on that specific race, a quick charge of the race, class, some bag slots, and they've got all they need to continue playing on a free to play option. As always however if they never wished to spend a penny, then they are free to continue as they want playing in a limited fashion, which a good portion of free to play gamers are happy with.
That is the subscription models section of the post taken care off, now onto the item shop that I would allow in game. The unique difference is that everything purchased from the item shop can make its way from one player to another through in-game trades, no bind on account. This doesn't take money from the developers, but gives the whales the option to spend their cash and sell on these items for in-game money. (Yes it is purchasing gold in effect, we do however move gold purchase in-game and kill off RMT from third party.)
Items in the shop would not be allowed to sell things like..
That's everything! Now I love my subscription based games, I prefer them over all else. I like a flat rate no fuss kind of game. What I get from this system is exactly that. Everyhting the game offers I can have without paying more than my subscription. The values are there for the other pay options as well however, with the free to players happily enjoying the its they want without spending to much. The whales get rich without creating a pay to win system, and those who create they subscriptions can pay for the small amount they want for a short time and enjoy just as easily.
The only play time that doesn't win in this model is the Pay to win gamer, with no options of buying power apart from the gold they could generate from spending money on shop based items to then purchase from other players the best equipment, this however is NOT pay to win, it's pay to progress faster, they'll still die just as easily as another maxed out character who didn't spend a dime in the case of the free to play gamer.