Can the new Cassiopeia W stop Ezreal E's?

A unit that is grounded is unable to activate mobility spells. i.e. all dashes and blinks. So yes, it stops Ezreal E. Hover over the word "grounded" in her W description in this link: http://leagueoflegends.wikia.com/wiki/Cassiopeia

All dashes, blinks, flashes and TPs are stopped by it.. so yes.

Yes it does.

sounds like it doesnt stop the e. it prevents it form being used. so if you w and he already e, then you miss.