Coronavirus outbreaks have been a growing concern. GDC 2020 was originally scheduled to take place in March. However, many companies, including Sony and Microsoft, have decided to opt out of the event. This, combined with the growing concern for the coronavirus, resulted in an official announcement from GDC staff. GDC staff said that "after much consultation with our partners in the game development industry and the public around the world, we made the difficult decision to postpone the Game Developers Conference in March".
As for what the event will be like, the GDC staff says "we fully intend to host a GDC event in the summer soon. We will be working with our partners to finalize details and share more details about our plans in the coming weeks." and the construction of Animal Crossing: New Horizons at GDC 2020. The company has not commented on the postponement of GDC at this time.