I'd do what Apple does. Sell my product to customers. For a lot of money.
I think they'd make a huge amount of money, on a recurring basis. And they'd be able to fund a lot of development. We could have a lot more than what we have right now. Twitter could fan out into being the Internet. This was the promise of Twitter at the beginning, until the company started to fight the natural inclination of a service like Twitter to fill every nook and cranny of the tech world. Instead, they fought to keep it small, so they could keep it under control and so (I guess) they could make money. But they had no ideas for what to do next.
But they would have to make themselves smaller, instead of making the product smaller. Sell us our handles for $50 a year. But don't do that until you can offer premium stuff that gets people excited. A little money is no big deal if you've got something that excites us. Apple has proven this over and over.
Instead of being a marketing company, selling us -- be a tech company and sell to us.
Twitter still has a product a lot of people want. That might not last forever. Strike while the iron is hot. Make hay while the sun shines. Yadda yadda.