I've proposed a similar system in January or so. The problem is, that one could have fun playing say in the Silver league and there is not as much frustration and pressure to buy booster packs. For this reason, I don't think they will allow such a system.
Game is designed in such a way as to push players to buy more packs through the frustration of losing to players who have spent on the game more.
Just my interpretation.
EDIT: In December last year:
https://steempeak.com/steemmonsters/@hotbit/league-format-improvement-proposal-and-discussion