It's already on PS Plus Premium, as the original PS.Blog post also states.
Draugoth
didn't quote the entire article in his post.
Sony's streaming works very well these days. I played through the entire game of Ratchet & Clank: Into the Nexus on PS Now about 2 years ago. More recently, I've been playing Sly Cooper and the Thievius Raccoonus in The Sly Collection on PS Plus Premium streaming. Both of those games are quite playable.
That said, I think Sony should've dusted off their PS2 emulator for PS4/PS5, so that they could give us the PS2 versions instead. By doing this, it would create a new PS4/PS5 executable package which would (theoretically) be more "future-proof" if subsequent Sony systems continue to evolve from the PS4/PS5 architecture. It would also enable the user to choose either downloading or streaming, as opposed to the current setup where the PS3 games can only be streamed. The PS2 emulator also allows them to run the games in higher resolutions, and use PS4/PS5 OS features like screen shot/video capture, Remote Play, and SharePlay.
Sony should have also done this (use the PS2 versions) for the games in The Sly Collection, and should consider doing so for other games such as the God of War series.