Just an idea......

Skill runes to upgrade skills. From simple twinks like reduce charge time, increase damage/dot/aoe, additional enemy hit etc. To more powerful runes like chance to adds status effects (stun, slow, bleed, reduce armor/dmg/speed, charm etc.) Basic attack runes like increase charge speed, attack speed, weapon proc chance etc. Rune power can be upgraded with gold increasing cost the higher lvl we upgrade also add a chance to fail that also increase the higher lvl the upgrade (to counter hyper inflation perhaps :/). Maybe the runes can work like gems that we socket to skills and can also be removed be it free or for a cost and transferred to other skills. Also some skill specific runes like for example skywards smash rune. Enemies hit will have a chance to get pulled to the center. Sorry if my idea sounds dumb. I just thought it would be a great addition to the game for a major update and it would certainly give us players more control on building characters depending on our own playstyle. Maybe this would also bring back pvp and make harder maps more manageable. Just my thought. Thanks for reading :D