In all honesty, I'd be very much ok with seasonal updates rather than monthly or weekly ones...
It would go a long way in reducing rushed disasters such as Rise of the Red Axe, would see more fully developped skills instead of shells to be later filled in, and you're guaranteed to have at least one jewel of an update like a complete City of the Elves...
It would reduce the regular updates to mere maintainance and the odd Ninja fix.
The only thing they need to permanently have is a playable Beta for everyone (including F2P-ers, since Beta's are meant to be experimented with beyond breaking point) that, like the EoC-Beta, can allow you to import an account without having it affect your main on the actual servers...
Membership revenue, however, would drop by two-thirds since a lot of people will just buy a months of membership when the update comes out, and cancel it for the following two...
On the plus side, the crybabies who can't handle a lot of changes (I'm looking at you 07&Legacy-lovers) get to swallow one pill every three months, rather than 4 a month...