If there will be another Mario stage, I really hope they don't make a 3D World/NSMBU stage.
3D World is made too recently, IMO, to be granted a stage rep, especially when the 3DS Mario stage is already a blend of NSMB and 3D Land. (I know Windy Hill Zone is from the recently new Sonic game, but, contracts.)
If anything, they need to give deserved attention to a Mario series that hasn't been represented as a stage (or via playable character.) Mario & Luigi RPG and Paper Mario being good examples.
Also, people are writhing for a Bowser Castle stage.