I played him mid against an Ahri, game went extremely well, but I had way less kill pressure than before since she can easily escape the Q (whereas E was reliable damage). I have to say the benefit of having good waveclear makes up for the lack of kill pressure, as I got about a 50 cs lead largely from the new Q whereas on old swain I would have been pushed under tower and missed a lot of cs. So it's kind of a mixed bag his laning is less interactive as you cant' really hurt mobile enemies who keep their distance, but you can farm much easier. Then you can get a quick ROA + Zhonyas and be a monster in teamfights.
I think he works mid, but you can't trade with or kill most enemy mid laners very easily, but they can't kill you either really, since you can Q the caster minions from a distance and it will kill all 3, and you are pretty hard to kill with the ult healing and the hp per lvl buff. His build is also easier as you dont' need magic pen to heal off tanks with his ult now.