I think the topic is pretty self-introducive. I believe players should know key amount when they download a beatmap because. For example, if you play DDR you can't really play o2jam maps because of huge key amount and if you play Beatmania you can find 4K too boring (well, at least for me). So key amount should be displayed with difficulty as well.
Also with RBRat3's help there are many delicious high-dpi icons:
Icons can be scaled if needed:
Also with RBRat3's help there are many delicious high-dpi icons:
Icons can be scaled if needed: