Teferi vs. Hypersonic

[CbStrad]

So, let's say I have {Teferi, Mage of Zhalfir} on my board. My opponent drops {Hypersonic Dragon}. Which ability would take precedence?

[Keyeto]

Teferi wins. Can't always beats can. And while Teferi doesn't specifically say can't, it's essentially nicer wording for "Can't play spells at instant speed."