So, I've got mixed feelings about this new rumor about the Speedway.
Regarding the Speedway, I'm firmly in the "replace it" camp -- I find it ugly, smelly, not in theme and using up a lot of prime real estate. I don't have a problem with the idea of a go kart ride, but the execution is poor and is nothing special compared to so many places you can find virtually anyone close to home for most people.
That said, I was getting excited by the hints that there might be a new attractions on new land instead of a replacement. MK needs additional rides, not just replacing what is already there. And there's plenty of expansion land, especially in Tomorrowland. DL constantly keeps all of its old rides and is creatively using its very limited space o add more attractions -- why can't WDW learn the same lesson? Furthermore, I'd only really support removal of the Speedway as a way to expand Fantasyland (since it encroaches on that land); TL actually doesn't have the same space constraints as FL.
Then again, this hinting is vague. Is this some sort of re-imaging of the Speedway to bring it more in theme with the rest of Tomorrowland (since the land is getting a refresh)? Electric cars? More futuristic vehicles? I'd support that certainly, but I think TL also needs an actual expansion and more ride capacity.