I want to play the Co-Op missions with my friend, but he's on the fence about getting LOTV. I know back when HOTS released Blizzard added a feature that made anyone in your party "own" your expansion for purposes of multiplayer. I'm wondering if that still applies to the Co-Op mode.
According to a post on Reddit it appears it is not needed to play co-op mode.
The key points in the post are:
The Co-op Missions feature is available for everyone, regardless of which version of StarCraft II you're playing. This also includes Starter Edition players.
You gain access to Swann, Vorazun and Zagara as additional Commanders if you purchase Legacy of the Void.
In a separate thread found here, a user says that if you party up with a friend that owns LotV, you get full access as long as you stay in party, so you'd be able to play the 3 commanders not included normally.