That's exactly what I meant by a campaign creator mode. Though I'm personally hoping it would also come with the ability to design a world map to place each level on. Like you create a world map that can be customized, but also has premade tiles or something like ghost house, and you could put your ghost house level on that, and your grass level on an area of the map that looked like grassland, or what have you.
I agree, a SMB3 or SMW World Map designer would be an awesome addition.
While we're at it, fake Bowser bosses like in SMB to get away with fighting him (and other bosses, like Bowser Jr, Boom Boom or the Koopalings) several times.
The Nintendo eShop rating Thread: http://gamrconnect.vgchartz.com/thread.php?id=237454
The Steam/GOG key gifting thread: https://gamrconnect.vgchartz.com/thread/242024/the-steamgog-key-gifting-thread/1/