I think he's still relevant in season 3 and I see him getting used in higher elos, but as well all know, playing him late game can be a challenge. I think most of my problems come down to my build. Usually I go:
Boots+3 -> Wriggles -> Avarice Blade -> Bloodthirster -> Statikk Shiv -> GA -> Usually IE or Wit's End
Probably too much lifesteal here and not enough AD? Also very squishy for late game
I'm also wondering how to properly engage with him in late game. A good adc/apc will have proper positioning behind their bruisers, as well as save their escape ability for my incoming attack in team fights. I pretty much have to rely on my team for a hard engage where I can then come in after a short delay to quickly finish a carry. But if we're behind, I don't really know what to do besides throw everything I have on the adc, pop my clone, and try to escape with my Q.