That would have taken over only the soundstage where the third Toy Story Midway Mania track is now (with an extended roof to accommodate several stories of coaster track.) The land behind it where Toy Story Land is being built was an employee parking area and backstage structures until recently.
I think it would've been better to have gotten a different ride than just a third Toy Story track... at the time. Now all bets are off and it's all Toy Story.
Rumors were that after the Monsters Inc ride was built, a smaller version of DCA's Cars Land was going to be built next to Pixar Place. That would've been three Pixar properties in a row... Now it's alllll Toy Story instead...
At least we're getting Star Wars too.
And who knows... some rumors are that Monsters Inc will be coming to the Animation Courtyard area after all this time anyway. So, that could be cool.
Until then... not many rides at the park. And there could've been one more than there is... but instead they just cloned the Mania track to get wait times down.