So here is a list of all the things that stood out to me as odd in the trailer plus what they might indicate.
-Toad and Boom Boom as part of Team Mario
It's not that they were seen in the background of an event or something where they could very well just be support members, they were on the podium with the other athletes and Toad's character flag is seen right behind Mario and Sonic. Toad is also spotted being treated similarly to Amy, Wendy, and Zazz in the Parade sequence. This implies that these two are now playable which would make this the first time the M&S rosters have diverged between console and handheld entries.
Furthermore, people have noted how some characters are missing that were playable in the 3DS game. Which has me wondering what other changes could be in store for us roster wise?
-That parade sequence
This trailer wasn't what we typically expect of the M&S intros as this one seems to have been made using in-game character models and locations as opposed to being fully cgi. However most of the scenes do use unique camera angles and added animation effects to create a more dramatic flair. The parade sequence doesn't do this however and actually neither does the opening pan of the athletes at the podium.
My thinking is that perhaps these two sequences are the beginning(podium) and ending(parade) of some kind of campaign mode. They just stand out to me as not having been altered where all the other sequences clearly have been.
-Dream events are like those in the 3DS version?
Towards the end of the trailer we get a glimpse of both a volleyballl match at night time and a soccer game that appears to be in the middle of the street. In the volleyball match we can clearly see item boxes implying this is a dream event and with the soccer game the location to me implies it must also be a Dream event. However both events seem to still be set in Rio. Does this mean we are no longer venturing into the Mario and Sonic universes for dream event locations? The 3DS version already doesn't so could the Wii U version follow suit?
So to summarize, to me it looks like we have reason to believe we are getting a unique roster thanks to Toad and Boom Boom, possibly a campaign mode of some kind because of that Parade sequence, and also we may not have the kind of Dream Event locations we have come to expect based on how the two events shown seem set in Rio.
That bit of speculation about Dream Event locations is going to bother quite a few people if it turns out accurate. Sure the Dream Events might be solid gameplay-wise but a large portion of the fun is seeing videogame locations reimagined to host these things.