I'm sorry but are you under the assumption that the old consoles will limit the new console? Here's how it works:
Make a model. Make several LODs. Implement LOD system to render at effective distances to reduce system load.
Make a texture. Engine will reduce memory consumption at the cost of asset load time based on impression and mops used.
Make a sound. Sound will be loaded into memory at the correct kHz depending on memory requirements.
And so on...
Thing is, you change these settings in the fly, depending on overhead. certain things willImpact performance more (such as draw calls and physics calculation and the like) but all of these can easily be increased and reduced in fidelity based on target spec.
the last of us 2? That can run on a pc from 10 years ago. You would just have to make sacrifices in a lot of ways. But all of these sacrifices are all entirely possible with just a sight change to asset distribution maybe, and a lot of setting tweaking.
Essentially, this is exactly the same way games work on X (the most powerful console) versus the S (the least powerful console). It's all a series of settings (Scarlet wants to render 60 AI? Make S render 15. Scarlet want to render 64 pass shadow map? S render 4. Etc), and tweaks. This is all something that's not only possible, but also easy, and done all the time.
There is ZERO reason this would change how complicated Scarlet games can be. I know you think CPU calculations won't be possible on older hardware, but even that can be scaled back with ease.
Source: Me, a pc developer. Who has been doing this same thing with asset control for over 20 years.