The rumored Teemo update will completely change the way he is played.

So as it is being reported these changes are essentially meant to turn Teemo from a top laner into a support. I will spare all of you the long backstory and just get immediately into what everyone is interested in;

A breakdown of each of his abilities and the rumored changes:

Passive - This will remain the same as far as going into the brush and going invisible. What will change is the removal of the attack speed buff. Instead it will be a move speed buff. For the duration of the move speed buff Teemo's auto attack or any other ability will apply a mushroom stack. Teemo can only apply one stack. After Teemo applies a stack any champion attack or ability applies stacks. At 3 stacks a special noxious trap is formed and armed immediately.

Q - The blind will stay as a single target ability. The damage will be nerfed tremendously especially at the later levels. Mana costs will change. This design is meant to make his Q a supporting ability rather than a huge source of damage.

W - The move speed boost will get buffed and also turn into a targeted ability. Teemo can use the buff on an ally and also get the effects of increased move speed. The ability will have a longer duration than currently and will allow Teemo and ally to move through units.
Teemo can also use the ability on an enemy as a slow.

E - This will be the most controversial as they are allegedly completely removing the "auto attacks deal poison" part of what makes up Teemo's identity. This is now simply going to be a toggled ability. Toggle one way and Teemo can use mushrooms to heal allies. Toggle the other way and they are noxious traps.

R - As you can probably guess, the damage from Noxious Trap will be absolutely gutted. It will still deal some damage but not a noteworthy amount at all. Instead the shrooms will apply the following effects depending on which one is thrown: Noxious Trap: Applies damage reduction and slow. The Ally Shroom: Move speed boost and heals for a percentage of missing health. After each heal the percentage is dropped drastically for a period of time so as to prevent an ally from running through 5 shrooms in a row and regaining full health. There will be no time limit on the number of mushrooms planted, however they are looking into a cap of 10 total mushrooms on the map at any time.

Obviously this will go through a ton of iterations and rewrites and testing and the planning is in the mid-early stages still. The expectation is do not expect any official announcement for months about anything, but DO expect these changes to his the PBE and go live before the end of the 2016 season!

Personally I think these changes are pretty awesome and I am excited for support Teemo. There is definitely nothing like him currently in support champions.