I think it would be cool to go back to Character specific boards again, and would like to see Boards incorporate iconic Mushroom Kingdom locations.
For Example:
Daisy's Getaway Voyage
This Board would actually be set on Daisy's Crusie Liner, part of the ocean, and a couple of small islands, with the Cruise Liner being able to reach these islands at different times.
Obstacles would include the rising tide, Cataquaks, Sushi, and giant clams.
The playable characters would all have Tropical Vacation attire on for this level(Hawaiian shirts, sundresses, snorkel gear, sailor outfits, swimwear, sun-screened noses, grass skirts etc.)
Waluigi's Pinball Park
This Board would be set in Waluigi's Pinball Machine(which it is now being operated as a sort of theme park which would clearly fail most safety inspections.)
There would be plenty of hazards to avoid and obstacles to set loose on the competition, and even a space that would allow you to play a brief bout of Pinball on the machine in order to steal coins from your rival players.
The playable characters would all have costumes that are part Tron parody and part roller derby(helmets, knee pads, chest plates, funky glasses, roller blades, etc)
Birdo's Dream Factory
This Board would be set in Subcon from Super Mario Bros. 2, and would be based on the factory-like levels from that game, although this one would be primarily focused on the assembly and boxing of fashionable accessories such as Pink Bows and Fancy Rings.
Conyer belts, Sparks, hanging chains, and Snifits would all be obstacles and features of the board.
The playable characters would be dressed in working gear.(Hard hats, tool belts, welder's masks, aprons, safety googles, etc.)
Rosalina's Bedtime Story
This Board would take place in the pages of Rosalina's famous Story Book! Players would be able to flip a page back and forth to change between two board layouts. A pop-out castle and village would feature on one layout and a dark forest and dragon's cave on the other.
There would be plenty of Paper Mario shout-outs on this board, like Hooktail living in the cave.
The playable characters would wear costumes based on classic fairytale characters.(Knights, Wizards, Robin Hood, Rapunzel, Little Riding-hood, etc)
Toad's Pit Stop Stadium
This Board is set in the middle of Toad Park, and is themed around a functioning go-kart track. Obstacles would include drivers in go-karts, oil slicks, and loose tires.
Depending on the turn, spaces on the racetrack become very dangerous to land on due to races suddenly starting, bringing the chaos of a typical Mario Kart race into play.
The playable characters would wear costumes themed around racing.(Race car helmets, jumpsuits, grease stained hankerchiefs, etc.)
Bowser Jr.'s Battle Playground
This Board would be set on an updated Block Fort from Mario Kart 64. The Fort would appear to have been turned into Bowser Jr.'s personal playground park since then, with the little rascal holding a pretend war there.
Obstacles would include Bullet Bills, parachuting bomb-ombs, Cannons that the player can launch out of as well as slides and sandboxes.
The playable characters would all wear amry themed costumes.(Metal helmets, camo, facepaint, walkie-talkies, boots, etc.)