That changed during the opening of Monday Night Raw in Oklahoma City, during an appearance from WWE champion Brock Lesnar. His advocate Paul Heyman formally announced that Lesnar would be entering into the Royal Rumble match, and that he would do so from the number one position.
There was no mention of Lesnar defending the WWE championship in said Rumble match, so that doesn't seem like it's happening.
This would mark Lesnar's fourth time participating in an actual Royal Rumble match. He won the 30-man gauntlet on his first try in 2003, after entering 29th.
During his second run with the company, Lesnar has been less successful, failing to win either the 2016 or 2017 match.
The card for the 2020 Royal Rumble, from Minute Maid Park in Houston, looks as follows:
*WWE Universal: The Fiend (c) vs. Daniel Bryan
*Raw Women's: Becky Lynch (c) vs. Asuka
*30 Man Royal Rumble match: Brock Lesnar (entering number one), Roman Reigns, and 28 TBA
*30 Woman Royal Rumble match: Charlotte Flair and 29 TBA