I think that most of these "chance on hit" only look good on paper but in practice they just don't ever work properly. For example, I had an unique bow with a chance to cast Shield Bash on hit. Awesome right? Well it almost never procc'd so that made the item quite dull. Then I had some item that had a chance to cast Unbowed on hit and the damn thing went off pretty much only when I was fighting a single opponent so it was pretty useless in the end.
So, instead of these "chance based items" I would rather like to see items with effects that happen on ability use.
For example: A bow with an affix "When casting Mark of Death, Walking Bomb will be cast on the same target". So when you use Mark of Death on a target it will also cast Walking Bomb on it for free without the animation (much like the existing chance based items like the Sulevin Blade). This would also be a way to make the less used abilities more desirable.
Additional item affix examples:
Using Caltrops will also cast Elemental Mines.
Using Evade will also cast Spike Trap.
Using Stealth will also cast Poisoned Weapons.
Using Fallback Plan will also cast Toxic Cloud in both locations.
Using Spinning Blades will now also cast Deathblow.
Using Ring of Pain will now also cast Blizzard.
Using Mighty Blow OR Korth's Might will now also cast Earthshaking Strike.
Using Challenge will now also cast Mark of Death.
Using Lightning Bolt will now also cast Lightning Cage.
Using Flashfire will now also cast Immolate.
Obviously there are quite a lot of interesting possible combinations. Also in addition to this kind of items I would like to see more items that work like the Longbow of the Griffon. How about an unique staff with an effect "Weapon attacks will hit all enemies in a 4 meter radius". Or a unique AoE dagger with the same effect? Nobody uses AoE daggers but I would imagine some would use a dagger that has a very large AoE cone.
There's lots of small details that would have to be figured out before adding these types of items in game because some of them could be simply too powerful. I think these types of unique items would be more fun than just simple chance based items.