An idea i’d love to see implemented 
Killing all enemies in an area, gives an experience, gold, item, gem, rune bonus, one or several.
Killing all enemies in an entire act, gives the same bonus, just greater.
Killing all enemies in an entire difficulty (all acts), gives the same bonus, just even greater.
Softcore gives lower bonus than Hardcore.
Bonus is given when talking to Cain, so that every player gets their own rightful bonus.
An idea is; Completing an entire act, gives runes for a random runeword; Mid level runeword for Normal, mid-high level for Nightmare, high-level for Hell.
This would make the game a little bit easier for those that find it hard to level and know the game’s mechanics. Easier to level up and progress.
It would also fight botters. Make it easier for people to find their own stuff, so that they do not buy things from botters and cheaters. Fight the dishonesty and make the game more fun and rewarding for honest players.