A couple weeks back, Nintendo's Doug Bowser mentioned Nintendo's presence at E3 2020 during an interview with the Hollywood Reporter.
"We look forward to participating in E3 2020. It is one of many ideal venues for us this year to interact with people in a social and immersive environment. Every year, we base our approach to E3 on the content we have to share."

Following that, the ESA has put out a press release today that reconfirms what Bowser had to say. Nintendo will indeed be a part of E3 2020, although specific plans have not yet been announced.

The Entertainment Software Association (ESA) today announced that registration for E3 2020: EVERYONE PLAYS will open February 15 at 11:00 AM EST, exclusively at www.E3Expo.com. The show returns to the Los Angeles Convention Center from June 9-11, with an industry day on June 9, followed by two days open to all badge holders.
E3, the world's premier event for computer and video games and related products, has been reimagined to include new stage experiences, experiential zones, and live events to showcase new titles and innovations in video games and to celebrate video game culture.

E3 2020 will feature special guest gamers, celebrities, and digital programming on the show floor while connecting with global audiences through extended livestreaming. A highlight will be the debut of an all-new floor experience that will be streamed to bring exclusive conversations with leading industry innovators and crea...