I'll put my Imagineering hat on as the song "the magic is in you" is fine but it's a testament it isn't in Disney Imagineering anymore.
The 50 years WDW show in Magic Kingdom should be in 3 parts.
1 How it started:
We hear Walt's voice as he pitches WDW on the tv special. During that we see the castle being sketched in black and white. We see a steel frame getting in place and Mickey building the castle brick by brick but soon we have many Mickey's building it to completion. During that sequence we start to see small, white fireworks that slowly get more. When the castle is finished it's in full color and the sky is lit with a lot of colorful fireworks.
2 The attractions:
We get the voice of Marry Blair and see It's a Small World as it would look as it was build as a castle. Sections of the castle open up to see the dolls from the ride and we hear the music. Fireworks matching the music and the tone of the attraction will be complimenting the visuals.
The same goes for Pirates, Haunted Mansion, Peter Pan (look Tinker Bell!), and on and on (at least one segment from each land of the park and one former Imagineer as a voice).
3 The Future
We want to thank you for your support and keep Disney in your harts for over 50 years and we will go for at least another 50 years! Who knows what the future will bring? We hear say that Walt said the park is never going to stop changing, that it never will be finished and we will keep that promise.
We get a Princes and the Frog Splash Mountain sequence and a Tron sequence (cool).
Then we go back to the castle, sparkling with a ton of firework and the end song based on the dedication text for Magic Kingdom.
Now start crying and buy the bloody t-shirt.