You can already see this happening with APB, although a bit more MMO'ish than a traditional shooter multi-player they are suffering from people just hating the multi-player game in the trail version and getting very poor subscriptions.
I agree that being subscribed would make players more likely to play the game as they have a financial commitment, and its wasted if they don't play. Conversely I expect this tacit would severely reduce the market as players will be much less likely to try the game.
Even if overall one time buy and subscription multi-player games make the same amount of revenue I expect there would be a more negative psychological effect with the subscription as the game frequently demands more money, where a one time cost, perhaps considerably higher, but once bought the player can forget about this and just focus on the game.
And like Pazur, I very rarely buy games when they are released. I don't spend a large amount of time gaming so usually have a buffer of a few games to keep me busy for a few months while the new releases drop in price.
