Including some possible online play
http://www.nintendoworldreport.com/news/64711/treehouse-at-nintendo-live-shows-new-super-mario-bros-wonder-gameplay
This weekend's Nintendo Live show in Seattle has shown more gameplay from Super Mario Bros. Wonder following this week's Direct.
The gameplay showed both single and multiplayer gameplay - including two and four player local-cop and some online methods being shown as part of the stage. The roughly 20 minute video can be found below:
Nintendo is also streaming tournaments at the Labor Day weekend event, although the Smash Bros Ultimate tourney was a team-based (Squad Strike) tourney.