While I think Tomorrowland speedway is:
1) Dated (you can find better go-karts in most big cities and most tourist attractions that don't go super slow and don't have rails) .. Just look to
LEGOLAND for a toddler and elementary age versions of go-karts at their Driving School attraction (and takes up a lot less space).
2) Takes up WAY too much space.
3) Has low capacity (especially for the space it uses)
4) Is not really "tomorrowland" themed in any way.
5) Doesn't "feel" green with all those smelly fumes going over the place. (Though it realistically doesn't take much gasoline).
6) Not unique - Every theme park I've been going to since the 80s (King's Dominion, Six Flags, etc.) has had some version of this attraction.
The fact remains that I don't think MK needs anything right now. It is quite busy without it. So I don't see them spending money on another top tier attraction/coaster at MK when the other parks have severe lack of attractions still (including AK despite the addition of Pandora).
They will focus their attention on Epcot next to help distribute the crowds between all four parks.