Singed needs a rework to his "toxic" playstyle
Singed is in a really poor spot. Rarely seen, easily countered, doesn't contribute well to team fights, and promotes a toxic gameplay style (pun intended). Only dumb players ever chase a Singed these days, and those are in short supply.
IMO, Singed would need more than a buff to get back into viability. His kit needs a rework before he gets back into shape.
My first stop on such a remake would be changing Insanity Potion. I'd do something like this: remove some of the stats it gives (i.e. HP regen), but cause it to instead upgrade his other abilities while active.
Stuff like this:
Poison Trail: Wider and is emitted around him (ala Immolation).
Mega Adhesive: Snares enemies briefly upon touching the slow field.
Fling: Kills and assists refresh the cooldown.
Of course, those are just rough ideas. If you've got better ones, post them up.