Yup had someone not technical tested their 300mbs service with wifi (and not ac) they were disappointed when they got less than a 100 mbps, we asked them to wire it to the modem to test again, they said 'but my computer is new'.
However, I'm more afraid of the people who do buy the service and use it to it's full capacity. There's a few that have legitimate use for large data transfers working from home. For normal users, I'm not too concerned even if there's a spike in the beginning there's only so much consumption that can happen at the moment. Meaning that sure you'll down load lots of stuff fast in the beginning but soon you'll be back to your normal consumption as there's only so much content out there. Now agreeably there's a rise of usage on the average per user. But then why would you buy more bandwidth if you're not planning to use it?