In addition to the "natural" improvements such as a faster and more stable PS Store, I see 3 features with great potential if they're properly supported.
1. Control Center Cards: In theory, these cards should make it possible to access the desired part of a game directly without booting the entire game to main menu. When I want to play TLOU Factions, I must first boot the game to main menu, then select Multiplayer, wait while it's connecting to servers, select which mode to play, then enter lobby and start matchmaking. Cards could potentially eliminate all that and go straight into matchmaking in the desired mode.
2. Picture-in-picture: This feature will allow you to see your co-op partner's screen. This brings back some of that couch co-op feeling, as you can follow what your buddy is doing while playing. It's relevant in an age of social distancing, and in an age where fewer and fewer games support offline co-op. Also a positive for people who like to watch Netflix while playing.
3. Game Help: I've seen trophy and achievement hunters being quite hyped over this feature, as for instance it gives you the ability to see where all the damn collectibles are hiding without having to jump back and forth between the game and a youtube vid on another device. If it gets more open further down the line so that users can share guides with each other, Ubisoft will find it very hard to sell those shady treasure maps for their games.