Precisely. Monetizing Twitter is a no-brainer if it has to happen. If the company runs out of money, they could do a token layoff of a couple people, issue a desperate plea to their user community with the headline SAVE TWITTER, and a bunch of us will pony up $19.99 a year.

I don't expect them to do that. There are all sorts of more subtle ways to bring in money, and I expect that they will try all of those first, serially or in parallel. They're trying to be very sure not to set a price so high that they can be undercut. If they avoid that mistake, they can own their niche for a decade or more.

It's also obvious why we haven't seen any attempts yet: Twitter is still recovering from the effects of the Fail Whale phase.

Now that Twitter operations are stabilized, I believe they still have a bunch of smaller competitors. It would be a mistake to drive traffic to those competitors by inelegant monetizing. It would be a better idea to let the competition die from lack of oxygen first. It would be even better if some of Twitter's competitors, driven by necessity, were compelled to experiment with charging money before Twitter does. Some of the best market research is that which your competitors do for free. And, best of all, one of the competitors might succeed in finding a monetization model that can keep them alive... and then Twitter can copy that model, but with a massive advantage in network effect and scalability.