I hoped for Zen 3 CPU cores, but I guess it couldn't have been mature (and cheap) enough for Sony's needs if production is going to start during 2020.
Same for the GPU.
Anyhow, both should offer a big performance increase from PS4, both plain and Pro, if RAM will be large and fast enough to use their potential.
Like others I guess too that the SSD will be in addition to a normal HDD.
BC is quite natural, CPU and the whole system are compatible evolutions of the previous architecture, they can offer at least the same BC of a new PC, with the advantage of a very limited set of different HW to set up, usually just one, with just different HDD size and SW and peripherals bundled on base and premium versions at launch and two HW configs if a Pro version is made later.







