The Mario x Rabbids thing would have been a cool surprise because it would've been completely unexpected, not because it's this phenomenal, groundbreaking concept.
Nintendo, for better or worse, lives and dies by the first party reveals. Now, they've shown their hand somewhat and we know Mario Odyssey is the big game. But last year, it was Zelda and that was still a good E3. As long as Nintendo has a surprise or two up their sleeves, E3 should be fine. The Wario World example is a prime example of Nintendo's hand getting revealed and blowing the show. The third party leaks shouldn't hurt too much.