As we are seeing at Worlds, teleport is one of the best summoners next to flash. It allows you to join a fight from anywhere on the map and leads to a lot of team fight situations that Riot also likes.
I believe it is time we go back to the idea we had in alpha phase, and from the Dota roots, and to make Teleport an item to buy. Either as a Teleport Scroll or a boot active. In fact, the same should be done to Flash, too. Currently, we are in a state of the game where there is always a stronger option. And instead of bringing every other option up to standard, Riot likes to just nerf everything instead. Flash and TP are good because they are fundamental to a 5v5 game on a large map. Time to embrace it and at least balance it. Either everyone gets it or no one does.
Bonus: Get rid of Stopwatch. It completely ruins plays, makes flash look balanced, and is only 600g. Not to mention, if you keep it, it builds into a cheaper zhonyas, which is perhaps currently the most defensive broken item in the game. You could build it on anyone and never feel like you wasted the gold, even if you're not an AP user.