The story expansion will focus on Alyssa Ashcroft.
Reliable insider Dusk Golem (aka Aesthetic Gamer) has reported that Capcom is already developing at least one story expansion for Resident Evil Requiem.
There is definitely at least one DLC in development for Resident Evil Requiem right now. I've heard about it several times, and the rumor is that Alyssa will have the main role.
Previously, the same insider claimed that journalist Alyssa Ashcroft (a character from Resident Evil Outbreak) will appear in the main campaign of Requiem: she is the one who, as a huge monster, chases Grace in the trailer, and at some point, the player will even be able to play as her for a short time.
When asked by subscribers whether Leon Kennedy is the main character of Requiem or a secondary one, Dusk Golem answered evasively: he does not have the full plan of the game, but he knows for sure that Leon will have "very large levels — the largest in the history of the series".