Investor sentiment around developer tools in Silicon Valley is still broadly negative. I worked for 3yrs at a company funded by prominent valley VCs and, unequivocally, they were trying to get us out of the "developer tools" business and "sell more to the enterprise market". The subtext being, "developers don't control budget in real companies".
And I think there's a grain of truth to that sentiment. You have to realize how much Twilio is a company built against the prevailing Silicon Valley wisdom of "how companies are built". These guys have a bit of a counterculture narrative, of "we're a developer tools company, we're growing, we're having a successful IPO, see, it can be done".
I, for one, think it's a great, harmless PR stunt. :)