In a presentation released for Sony's "Investor Relations" day today, Uncharted 4, previously a PlayStation 4 exclusive, appears on a slide under the heading "More PC releases planned." Also on the slide is Days Gone, which hit the PC just last week.
The slide, labeled "New Growth Vectors," shows PC releases as a way for Sony to increase the return on investment on existing first-party games and "create new fans for our IP."
Considering Sony's past statements that it plans to bring more games to PC, this one isn't a shock. But Sony seems to have leaked this particular planned PC port in its investor report ahead of an official announcement.
Sony is streaming a State of Play event tomorrow where the first Horizon Forbidden West gameplay will debut. It's possible the announcement will be made there, but that's just a guess.