No exact date has been given yet. But it is expected that the PS5 will be available in the market by this holiday 2020 i.e. by the end of 2020.
Maybe in the month of November or December, it might be available.
On comparing PS4 with the new PS5, the upgrade is worth it as the specs and features tell.
It's going to be the world's fastest console, which is a significant upgrade over the PS4.
The most important one is the faster storage due to the SSD. Also, it has a whole new architecture, superior resolution support. Few specs comparison of the PS4 and PS5.
Sony has added and improved the capabilities of its platform in every way like adding more storage, faster compute parts, support of larger capacity disks and support for higher resolutions.
PS5 has 16GB GDDR6 memory whereas PS4 has 8GB GDDR5.
Internal Storage: PS5 has custom 825GB SSD and PS4 500Gb, 1TB HDD. (SSD makes it faster and different)
Optical drive: PS5 has Ultra HD Blu-ray whereas PS4 has only blu-ray.
Hence video output of PS5 4K at 120Hz, 8K and PS4 has only 1080p.
These might be helpful.