As will all other suggestions about ways to get diamonds flowing into the economy, I have to object only because putting such a high value, time capped, hard bottleneck resource in only one repeatable source will overcentralize gameplay and induce extreme burnout, especially if people don’t happen to inherently enjoy the mode. In other words, even putting 10 diamonds in there for a potential half hour slog would make this mode the best use of my time to the exclusion of other modes (beyond about 40 PvP battles/week), and running it hundreds of times when I don’t particularly like arena (and I would, and so would others) would just cause me to just hate the game.