If I was running the iOS App Store, I would send out a letter to every App Developer, informing them that Apple is now charging $299 USD per app, to keep apps in the App Store, and that payment MUST be received no later than 30 days from today.
That simply act would force Devs to do the clean-up, & I'd bet, cut down on the Garbage Apps much faster than any other action Apple could devise !
In fact, I'd bet that 90% of the Apps would simply be left to die (by their Devs).
So, Apple would make $299 on the remaining 10% of apps, but the intend is NOT to make Apple extra Coin ... simply to position the clean-up appropriately.
It's NOT Rocket Science, the iOS App Store could be COMPLETELY cleaned-up in 30 days !
And of course, an App Developer could always RE-instate an app past the 30 day point if they couldn't come up with the necessary Coin by then, or changed their mind after the Deadline.