Moreover, the inherent problem with a random drop system is that luck is just dumb, making the system itself dumb. Playing the lottery may be fun for a while, but it has never been considered particularly smart.
Last, the current itemization issues make for both gimmicky and non-RPG builds. For example, all the top-dps monks and DHs use exactly the same gear combination. Set items especially are often not good enough in themselves to compete against best-of-class legendaries and people just give up on complete sets.
Introducing Paragon 100 drops.
When one reaches Paragon level 100, instead of getting regular legendary items, on should have a chance (equal or maybe slightly lower) to get a "Paragon 100 drop", that is an account-bound drop that uses one the char's equipped items as a baseline and then improves it.
Because those drops would be account-bound and require paragon level 100 to be equipped, they could only be used to improve the current char or another char brought up to level 100.
But they would replace dumb luck with smart luck and:
-- Allow great set items, legendaries or even rares to become better still and help make sets more appealing, because you'd need to have your Nat's Sight or Inna's Favor equipped to hope getting an improved one with added or upgraded affixes. A Nat's Sight so improved, adding IAS or combining CC with all res (which are mutually exclusive right now), could become competitive once again with a Mempo for instance.
-- Make people want to keep on playing after reaching Paragon 100 because all of a sudden they'd know that _will_ get upgrades if they keep at it. No need for the AH and mountains of gold any longer. Upgrades _will_ drop. Just keep playing and having fun.
-- Make people want to bring more than one char up to Paragon level 100.
-- Make for truly unique heroes, because each Paragon 100 drop would be truly unique, improving on an already great item in new ways. Any helm could carry IAS, or movement speed, any belt CC or CD etc. A Calamity could offer both DEX _and_ a socket. LS could belong to any item, not just weapons and Barb's belts.
-- Remove the constant suspicion that the random drop system is meant to force people to use the RMAH to buy gold and make Blizzard money that way, because upgrades are simply impossible to get through actually playing the game. With "smart" account-bound drops, one can get upgrades by simply _playing_ D3. Finally!
Using the same logic, Hellfire rings, when crafted by a Paragon level 100 char, should replace the 35% xp affix with a useful one: 9% IAS xor 6%CC xor 50% CD. It would give players an incentive to craft new ones because a really great one would be that much more probable.
I hope you'll find those suggestions useful.