Leave it the way it is. It matches a lot of the games out there in price point that provide roughly the same style of service. F2P games require a "leveling" system of some sort to make you want to pay. If that expansion HTC's been working on forever (Combat Tour? Theater? Whatever the last interpretation was) ever comes out, perhaps it could be done there as it's more of an RPG in the sky. For the current Main Arena system, though, I'd absolutely hate to see it. The premise of the game is that, when everybody takes their tinfoil hat off, everyone is as equal as the game can make them. Everyone's plane takes off under the same conditions with the same stats. A F2P/Pay for More game can't work under that philosophy, because the people that pay want to be able to steamroll the freebies.
As to what I'd like to see...I'd sell my firstborn to be able to keep my account whenever I need to skip a month. I've never understood why their account management is so clunky.