1) BROADWAY LEGO SETS
I'd LOVE to own a RENT Lego set, with three separate actual location sets: There's the community block with Benny, Mark Cohen and Joanne, the dining area below for Roger, Mimi, Maureen, and the street side alleyway for Tom Collins and Angel (with drum set of course)!
Or can you imagine a Sondheim collection? Into The Woods LEGO set? Sweeney Todd LEGO set with meat buns unique lego tiles? Or even A Little Night Of Music?
Or a Broadway's Greatest Collection with a Les Miserables set. Or a Phantom of the Opera set. I know I'd love to see a The Lion King set too!
Maybe the sets can come with the CD of the soundtrack of the musicals, to be a good entry point as well for kids to appreciate musicals?
2) Post Apocalyptic LEGO
Can you imagine a series of LEGO kits that allow you to recreate scenes from movies like Mad Max or the future in Terminator? LEGO sets that have bricks that can be used to create damaged and worn down looking models? Bricks with "broken" portions and exposed wires. Tiles with shattered patterns on them. Maybe even rusted colored bricks and warped glass panels.
3) Steampunk LEGO
Sort of like a LEGO that is halfway Technic and halfway still basic LEGO. Gears and pulleys as normal pieces. Chain links as a common means of interlocking pieces. Tiling that can work as both patterns and building tools. Screw and bolt connectors.
4) Horror Greats LEGO kits
Can you imagine how a Jack the Ripper LEGO kit would be just awesomely cool? Or a The Frankenstein Monster set complete with Dr. Frankenstein laboratory? A Dracula kit with Brides you can have walk on the walls? My favorite idea: I would LOVE to own a Freddy Kreuger LEGO kit.
But man, I'd love to see these happen someday.