The idea is pretty simple. Make damage over time abilities and debuffs scale a lot better. Often DoTs are used as combo starters or for other debuffs, such as the rogue shadowstab bleed that leads to the grievous wound for the final hit in that combo, or the use of the warlock/mage DoTs that give the soul brand debuff. The enchancement of damage over time debuffs would increase classes capable of doing endgame by a decent amount. Obviously most of the class combos that rely on damage over time are magic classes, such as priest/rogue, warlock/x (mainly wl/r lol), mage/rogue etc as well as rogue/warrior which has I believe 5 total damage over time debuffs. When I say scaling better I mean increase the damage they do so they aren't just used for the debuffs that come alongside or to create attack combos. An example of a really good DoT is the one that the dragonflies in the chamber of elements (and maybe in inferno I dunno) give which does to me about 22k every two seconds. That is what I would call a good DoT, and it is a lot better than the ones I can do with any class combo which reach about 8k every 2 seconds. You can most likely see why 8k every 2 seconds is worthless when my psychic arrows in the same state do about 1 million each hit, and each casting of that is 2 seconds.
For those who didn't wanna read, make damage over time better so I can play warlock/rogue in endgame... lol.