For me they still can. Sort of. The others have wowed me so far with 1 or 2 announcements in their shows:
- Bethesda: Fallout 4
- Microsoft: Rare Collection, Backwards Compatibility
- EA: Unravel
- Ubisoft: South Park the Fractured but Whole
- Sony: The Last Guardian, Shenmue III
So... for me it takes 2 to 3 megatons for Nintendo to win E3... conference wise.
On the other hand, because they won't have Fallout 4, Unravel (maybe?), and South Park, they almost can't win in terms of the number of newly anounced games that will come out in the near future that I'm looking forward to - of course I'm not counting Xenoblade X and Zelda (which I'm super excited for!), since those have already been announced.