Sorry if this has been brought up already but I think the main reason they did decide upon Click and Buy was because of fake credit card frauds. Since a person could play for a month or two and then lie at the fact that their credit card wasn't suppose to be used and such so they end up getting reimbursed. Because of this not only does SE lose money from the customer that did that but I believe they also pay additional fees cause of it. The kinda stuff that does go on with CC is bull but you gotta blame the people that exploit things like that. For a proper payment system though it does seem like it would be logical to have Crysta cards that they sell just like psn xbox and other game cards. But maybe they fear that they production and the fact there isn't a lot of stuff that crysta can do atm will show in it's loses from the production of the cards.
I'm not even sure what would be the best method for Monthly subscriptions they all seem to be exploited in one way or another though I do hope that by the time they do decide to make it a monthly subscription they add another payment method. If anything maybe they'll allow crysta to be purchased with psn network so then you can get crysta that way which would be nice. Though that's the only other way I can think of doing it atm other then using old systems that seem to be exploited by some.