One idea to incentivize use of golds and low diamonds in ranked would be like a low risk / high reward system for ranked teams with lower overalls. For example, a player using a diverse team with like 90ovr would rank much faster after a win and take a smaller hit after a loss. A sliding scale based on team ovr could be implemented so that an elite player could shoot up to WS much faster if they're good enough to win with an inferior team.
Another idea is a new multiplayer game mode that combines ranked and BR. Players could create custom teams under BR style restrictions (X amount of high diamonds, X amount of low diamonds, X amount of golds/silvers etc). I feel this would be incredibly fun and would allow players to utilize underrated cards in balanced ranked play.