Revenue: Twilio made $166M in 2015. From Q1 2015 to Q1 2016, thew grew 80% -- so we can project a 2016 revenue of around $300M. At that pace, they'll hit ~$1B in 2018 or 2019.
Landscape: They have very few competitors, in constrast to other high-profile enterprise startups like Box.
Cost of revenue: Their cost of revenue -- servers, telecom bandwidth, customer support -- is ~45% of revenue. Typical SaaS startups run around 20-30%. I suppose this is the danger of being in the telecom space -- you do have high data costs.
Sales & marketing: Coming in at ~$50M, or ~30% of revenue is quite reasonable. Box raised concerns a couple of years back when S&M were 125% of revenue; they were able to get it down to 65% or so and then they IPO-ed. 30% is fine.