Wtf, they said that all the textures details and tessellations are streaming as you are turning around. You don't understand what you're saying.
Tessellation doesn't "stream" it's done on the GPU to add model details in real time (to save on the need to stream assets).
The point of the streaming speeds is to avoid the need for tessellation and other "fake" details.
They could use slow HDD on something with much more VRAM. The fast SSD is needed because of other deficiencies. Get rid of those and it's not required. (For fidelity)
With enough VRAM you could load complete games in memory. Seriously, what you say is technically true, but there is a point where it becomes unpractical, the loading times for a game that needs 50GB for a given area are going to be atrocious on a 200MB/sec HDD, or a 533MB/sec SATA SSD (assuming that there is no need to stop for processing).
Now how much data would you need to precache for a game where the gameplay is open ended, if you want the exact same experience?
Nope, they never said that. He also says that they could technically do this on a PS4.
It's a PS3 game at its core, the PS4 could very well have gotten an improved remake, not as extensive as the one we got, but a game that has the same gameplay elements would certainly be possible on the PS4.
I'm never sure what people argue about with the dark souls remake.