Last November, Riot announced that they would be overhauling League of Legends' systems for rare and exclusive contents, including Prestige. However, they recently announced that they cannot meet the original timeline; meaning they have expanded the list of Prestige skins.
We've seen Lunar Beast Fiora Prestige Edition, and Battle Academia Leona Prestige Edition is available right now; with Space Groove Lulu Prestige Edition on the horizon.
Sylas and Pantheon will be getting Prestige skins later in the year, for unknown events. Being 'events', these will include a Pass which will give a way to get Prestige Points; as well as being a larger mark on the League of Legends calendar.
Conqueror Jax Prestige Edition gives a little more of a time frame, as it will come out around MSI; which we know will take place in May. It also confirms that Jax is getting this year's Conqueror skin!
Finally is Zed, but for a previous skin. This raises questions at what it could be. My bets are on Project Zed, as we haven't had a Project event in a while and he was one of the originals, or Galaxy Slayer Zed as part of the next Odyssey instalment.
While we don't know what the skins are for the most part, it does mean we can start saving those Prestige Points! On the timeline released in November, Riot said the 2020 Prestige Points will expire in May (reflected in the client too currently). Due to the delays, this could mean the expiration date will be pushed back further.