Charge for reach. Ask accounts with more than 50K followers to either pay for all followers to receive tweets, or limit distribution to 50K followers, randomly chosen.
It's the accounts with many followers that get the most benefit from the platform.
And, a twitter crack could, in present circumstances, cause global political instability. The accounts with > 50K followers, if compromised, are the accounts that could cause this sort of problem. Why shouldn't the users of those accounts shoulder at least some of the cost of securing the service and making it fast?
Another possibiity: the Bloomberg Terminal biz model. Charge consumers of twitter for timeliness, and delay messages to unpaid consumers and general feeds. Allow originators of messages to purchase timeliness for their own messages, even to unpaid consumers.