As much as I hate arguing AGAINST nerfing Teemo, the nerfs to his shrooms are excessive and don't really get to the heart of the problem. Yes, Teemo's shrooms are a enormous problem right now, but that's because we have no tools to deal with invisible traps right now. The removal of Oracle's Elixir was the right move for long term health, but it also made AP Shaco and Teemo considerably harder to deal with. By nerfing the damage of Teemo's shrooms rather than giving his opponents tools to deal with his shrooms, you do nothing to get to the heart of the problem.
What we need right now is SOME tool to deal with invisibility, not nerfs to make Teemo unplayable (ohmygodIcan'tbelieveI'msayinghthis). Give us some kind of tool like Hextech Sweeper or Lightrbringer (although with probably reduced stats) that enable us to deal with traps and stop nerfing champions like Shaco and Teemo into unviability instead. I don't like Teemo or his playstyle, but all you're doing right now is making Teemo unplayable and that's completely unfair to Teemo mains.
For the record, I'd love to see Teemo's shrooms be reduced to a .6 AP ratio with slightly higher base damages (I've thought the ratio has been too high for awhile), but the current nerf to Teemo is unreasonable. Give us some tool to deal with invisible traps and if Teemo continues to be a problem afterwards, then we can nerf Teemo into the ground. But please, don't nerf Teemo just because your changes to vision gave him an unexpected buff.