There was evidence of the NSA intercepting international communications before Snowden, but for some reason that didn't seem to make much of a lasting impression: https://en.wikipedia.org/wiki/Room_641A

It's also significant to note that while the government is quite bad at keeping 'problematic' behavior secret, companies are much worse at it.

Analogously, there's evidence that companies will make extensive use of available techniques (browser fingerprinting, cookies, etc.) to track and surveil users without their knowledge and often against their will. The exposure of that arguably also hasn't triggered an effective backlash against those companies. So, as with the pre-Snowden evidence for domestic communication interception by the NSA, I think there's ample evidence of the willingness of companies to exploit whatever technologies they can in order to surveil users.