Nintendo's E3 presentations tend to be fairly game focused with only a few segments of their videos focusing on developers talking about their upcoming game. Nintendo Directs can be anywhere from 3 minutes long to 30 minutes long, but with E3 it's widely assumed that the presentation will be on the longer end of the spectrum.
As it turns out, Nintendo's E3 'Spotlight' presentation will only be around 25 minutes long. It's unclear what will be shown during those 25 minutes, but it's fairly certain that we will see Super Mario Odyssey and Splatoon 2.
Hopefully, the 25-minute presentation focuses on Nintendo Switch games only, with another presentation or panel for 3DS announcements.