Teemo mid

It can work against ad champs who rely on autos and mages that don't outrange/burst him. The real value of teemo comes from having a field covered in shrooms giving you pretty good map awareness if you pay attention.

Not really, no. He needs to get his satanic ass in line for a full rework, but unfortunately Riot (and much of Teemo's playerbase) is stubborn. Almost as stubborn as the largely unjustified hatred of Our Lord and Savior.

It depend of whos mid...

Teemo counter veigar quite effectively. As long as the mid dont have a gap closer or you can dodge the skill shots, you could be mid. It clearly depend of your skills and what you are building.

But normally, I wouldnt suggest it, unless you play close to your turret and getting some ganks. Teemo is best mid game. If you get early gank, his speed can be quite effective to make sure you secure the ganks. And his shroom allow some warding and anti ganking midlane once you get level 6.

But before level 6, I suggest you play defensively mostly. Take Teleport to gank some other lanes and teleport to shroom, use his passive to your advantage and then it can be done.

He falls into the role of "you can, but why"

His main purpose in life is to annoy the crap out of the enemy team. Ideally this starts with him in lane with his E vs a melee champion with no reliable ranged farm. Most things mid can farm from a distance, so you lose out on one of the things he does best.