As far as how to distribute the hashrate from completed accounts, I don't know enough about how many accounts have how much in them to say what would be the best. Although another idea would be to randomly pay out to one account at a time (0.01 BTC) given to a random account at a time with some extra weight to larger accounts. Or split things between different plans 75% to n oldest accounts, 20% randomly, 5% to largest account). I'll be happy if I can get paid out in the foreseeable future.
As for favoring new vs old deposits, that's something that has to be done. If old accounts are favored there's no reason to create a new account, keeping some of the completed account hashing power in the new deposits even makes sense; faster returns is more incentive to add money into the system. If there's no new money there's no new hardware, this is something that should probably have happened for each successive generation of hardware. Getting MHs when you have to pay for GHs doesn't make a lot of sense and just seems like tossing more money into the same pit that took your money in the first place. People have to be able to profit off their own money and then everyone else can recoup "lost" money.
While I agree with the move to give new deposits the actual hashrate they ordered, I disagree with the new deposits need to be given priority. Old/New can be paid out in tandem.
Instead of focusing on the potential new accounts going forward we need to get the backlog cleared first. There are plenty of chained/nested accounts that would create new deposits that could be turned into new hardware. And as pyra already posted he decided on the earliest 10 deposits because they are the ones absorbing most of the referral bonuses. There is one account above me that deposited only a few BTC and has been paid out several hundred, I don't have a problem with that but to be honest losing 30% of earnings is a major factor in this current situation. If we clear out the deposits/accounts from the top down then all those ref bonuses start bouncing back downline and help clear out even more accounts.
As others have posted, pyra is the one with all the data to base a decision on. However, I still feel that splitting some or all of the excess hashpower to ALL current deposits would allow for accounts such as mine to move through the chain and put that money back to work.