I wouldn't worry about it. If you watch the first Rio Wii U trailer, it has Yoshi doing table tennis, Eggman doing Volleyball, Bowser Jr and Silver in soccer, among others. They couldn't do these in the 3DS version, so I think it's safe to assume there won't be that restriction
That's why I said "newcomers". All of the characters you listed are veterans.
The 3DS version limited veterans to two events, and newcomers to one. With Mario & Sonic being in all of them.
However, with all of the footage/screenshots of the Wii U version we've seen, they've specifically only shown newcomers in one specific event (Gymnastics for Rosalina, Volleyball for Rouge, 100m Dash for Nabbit, Table Tennis for Zazz, etc). The game is also coming out very soon, so that's worrisome.
And with Rosalina specifically, they probably would have shown her off in other events by now if she is in them, because she would have to have different outfits, like Peach/Daisy/Amy/Blaze for the different kinds of events. I doubt they'd let her go barefoot and in a leotard in every event if she is playable in all of them.
It's basically believed that the veterans will be playable in every event, but the "newcomers" aren't really newcomers. Instead, they'll probably just be rivals like in past games, but you can unlock them for their one specific event and play as them.
This will be especially confusing considering Rosalina and Rouge are on the front cover. I don't see why they put them there if they are going to have such minor roles. Sex appeal points, I guess.