Incredibly doubtful we'll ever see another way to get medals outside of grinding classic.

Vast majority of us who got our way up to Gold 4 and 5 did so the old fashioned way, grinding it out until we got to the area of the game where you can just farm easy lineups in G5. 

As well: this is a very PvP centric game, one I'd argue really tries to funnel people towards it. I could imagine a mission like Tag oriented ones being changed eventually but I can't see a decoupling of classic Arena and its importance to fleshing out stuff like the Great Hall & missions ever really changing.