I've been saying this for years, and I mean since 2007 or 2008, though I had figured just price levels. If you have 100K followers, that's probably worth some money to you. If you have 1M followers, that's worth even more. I was saying in the 2008 elections that CNN should have an entire rack in the data center sponsored by them, they were pushing their Twitter handles so hard.
One thing would be the fake followers, where you could DOS someone by creating bot accounts to follow people and use up their slots. I like the idea of randomly chosen followers, that's a twist I didn't think of; it also mitigates the issue of the fake followers. You could also do the opposite, charge to follow more than some number of accounts.
Now you're asked to pay to reach them? No way.
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.