So Riot finally decided that they need to do something about a champion that they have been struggling with since almost a decade. Better late than never I guess. Here's my thoughts on the proposed changes:
You don't have to do anything with Teemo if you just change his W to a quick dash with invisibility (like Kai'sa's E), and to account for this you take away his passive and change it to something like Fiddle passive, where if Teemo is standing still then he gets movement speed or something else, other than invisibility.
The current proposed rework actually makes him weaker, thanks to the slow on his E. Even a freaking Garen could now just press E and Teemo won't be able to escape even if he is camouflaged. What is the point of that E anyway? You want to create Teemo jungle or what? He can't use E to escape due to the slow, and he can't use it to chase, thanks to the slow again. He can probably use it in a fight against someone like tryndamere, but again, Trynd has never really been an issue for Teemo anyways. Also, don't you think it is kind of stupid to give MS with W and then suddenly slow down the same amount with E, basically making both the abilities useless?
The whole reason why Teemo is trolled around the world is because of his squishy kit and inability to escape. People see a person pick Teemo and think that now they will have to deal with a fed assassin or bruiser. Maybe increase his range as you put points in E? Here's what I propose for all the changes:
P - If Teemo stands still for 1.5 seconds out of bush (0.75 secs in the bush), he gains movement speed and increased attack range, both scaling with level.
Q - A skill-shot that blinds anyone in the path of the poison missile for 1-3 seconds as it spreads a poison trail in its path, doing damage.
W - Teemo dashes in the direction of the cursor while also being camouflaged. The distance of the dash increases with the number of points put in.
E - (passive) Teemo gains poison on his auto-attacks - same as before.
R - Either same as before or the changes that were proposed - both are good.
With this, Teemo's skillset is now harder to play because now he has to synergize his passive with his W. His Q is no longer undodgeable, but with the increased skill level it now also gives a greater benefit of blinding more than one enemy.