A new Super Smash Bros. Ultimate commercial includes an image of the game’s menu that may indicate a stage builder mode could be on the way.
The screenshot appears right at the beginning of the new Super Smash Bros. Ultimate commercial and the icon on the bottom right indicates the mode that was included in Super Smash Bros. Brawl and Super Smash Bros. for Wii U may be returning for the Switch version.
Source: IGN.com Smash Bros. Ultimate May Get a Stage Builder Soon