I'd wait for a SMW variation. Nintendo's infactuation with SMB1 is weird. I don't think it is anyone's favourite Mario game. It's historic and is certainly still enjoyable to play but it has been so thoroughly topped by its sequels that it's really a game for history buffs and completists today. If Nintendo did a fan vote for what retro style to use, SMB1 would almostly certainly NOT win. Hell, when I was a kid we all thought SMB1 was super old, when it was only like three years old at the time.
Of course SMB1 is a lot simpler than the later titles so I can see an obvious advantage for Nintendo to go with something simpler for a game editor, particularly when it's their first go at it. But that all goes back to my assumption that they wouldn't match the free editors already available from hackers.
I do like, however, that they're open to retro styles so that's encouraging for sequels or DLC. I was afraid we'd get NSMB style and nothing but.