The video I watched on the making of Horizon had  Guerrilla spend most of their time during the making of shadowfall utilising a small team to conceptualise what became Horizon ,all this really comes under the heading of pre production planning to the point that when Shadowfall shipped they started in earnest ,like they  themselves said 6 years  with full production taking 4 years. 

I was thinking exactly about this. The thing I know for sure is that they won't make it a cross gen game, it will either release on PS4 or PS5. Althought nothing is guaranteed, I think they'll want to save it for an early PS5 release. 

Imagine how helpful it would be to have GoW 5 releasing on PS5's first or second year? It would assure an extremely fast adoption.

I would skip GoW2 on Ps4 and release Gran Turismo instead.

PS4 - 1080p/30
PS4 Pro - 1800pCB/30
PS5 - 4K/60 + Higher Resolution Textures, Improved AA, Better Lighting, etc.

If PS4 and PS5 both share X86 and AMD GPU tech, it it extremely easy to support both platforms. I see Sony supporting PS4 for the life of PS5 and finally dropping support when PS6 arrives. This is nothing like supporting PS2 and PS3, or PS3 and PS4 where the game has to be almost completely rebuilt.

Of course it won't go multiplatform! What kind of question is this?

One of the considerations we haven't factored in is the new god of war 2 is a sequel meaning you could be seen as disenfranchising a large part of your audience from the first game if you move it to the new platform , and if it is say only 2 years and  PS4 sales hasn't done the unlikely and fallen off the cliff , you only strengthen that point , another option is to release it on PS4 then release a remastered version for PS5 of both games as an appetiser for GoW 3 for PS5 if they can spin it out to 3 games, also you might be better having your big hitters spread out from year two onward where new consoles tend to start to refine their schedule leaving year one to highlight other IP.

I can easily see God of war 2 being out by 2021. Sometime that year. Ps5 only would be OK and a major system seller. For the extra cash say ps5 launches holiday 2020, they might remaster god of war at 4k 60fps for its launch for extra revenue. 

In my opinion the same Nintendo did with BOTW by releasing it both on Wii U and Switch.

So for GOW 2 I think it should come both on PS4 and PS5.

Pretty soon with rising development costs and long Dev cycles, I doubt gow 2 comes out in less than 4 years from now. 5 most likely.

Example.

Only one uncharted game this entire gen.
One gow.
One Gran turismo.
Death stranding still isn’t out.
No kingdom hearts 3 yet.

With ps5 rumors starting to fly, it’s not long till next gen is here.

Pretty soon I could see us getting only one big installment per gen in each franchise.

There were two uncharteds?