Celebrating the Magic Kingdom's 50th anniversary with a Tron rollercoaster would be really weird though. If they're refurbishing all of Tomorrowland it would make sense, but Tron is the only thing we know is happening in Tomorrowland and the Magic Kingdom for the 50th anniversary.
I think Disney could do something extra, like a new Fantasyland dark ride. Disneyland has tons of cheap dark rides they could bring to Florida like Alice In Wonderland, Pinocchio's Daring Journey (or, you know, Mr Toad's Wild Ride). Tokyo Disneyland is building a Beauty And The Beast dark ride that could go near Be Our Guest.
If the main plan is to refurbish Tomorrowland, then they have to show what's happening to it at D23.