Warcaster doesn’t state that it changes casting time of the spell when you replace an OA with it like Quicken spell does. Could you use WC to reaction cast an action cantrip on the same turn you cast a bonus action spell?Yes.
— Jeremy Crawford (@JeremyECrawford) February 23, 2018
No problem!
— Jeremy Crawford (@JeremyECrawford) February 23, 2018