I don't think that the only path forward is an M&A since they have plenty of cash, good revenue, and a reasonable product strategy. Doesn't mean, like any startup with way less traction, they wouldn't consider one at the right price.
Google is saying no to paying $18bn (just under $15bn in enterprise value) for that. I have a tough time valuing it north of $5 or 6bn EV, and that's assuming $500MM in earnings within 6 years (and break-even in fewer than 3).
I was in their office last year, talking to people who had nothing at all to do with the core product. There seemed to be all sorts of APIs and whatnot that they are trying to push, all of it marginal in relation to what most people think of Twitter.
http://www.usatoday.com/story/money/markets/2016/01/25/twitt...