Psyonix has announced that Rocket League will get PS4 Pro support next week, on the 21st of February.
The new update will allow Rocket League to run at both 1080p (on a standard PS4) and 4K (on PS4 Pro) at 60 frames per second in all arenas for single and two-player split-screen modes. Three and four-player split-screen modes will offer 60 frames per second in most arenas at the same resolutions. This update will also bring the new fan-voted "Player's Choice" Crate filled with some of the community's favorite items, PS4-specific technical improvements, and multiple performance optimizations and bug fixes.
In addition to the PS4 Pro update, Rocket League is also getting the Hot Wheels DLC on the 21st of February.
Source: PlayStation Blog