That is then an optimization problem, or if not that, then it is the end on the developer side and its the player who has to get more gutted gear to play this game on, otherwise it truly is the end as computer stops serving frames all together at some point.
There are many sorts of high ends too... How big of a factory you can build that is as realistical looking as possible with all the supporting structure where trains dont go through the ground and not a single belt trough another.
I for one would not play this game if it was about just building larger and larger and then not being able to take care of the looks, the game is made pretty anyways. And i did quit for a while with my tower till the lift conveyors came, my god the horrifying conveyor mess...and therefore not being able to scale due to space limitation.
One of my bigger concerns is how to make a wire go into a building and come out of it without looking odd, that btw needs something too, a power wall maybe. And reducing image quality down from max is not a thing, thats how do i like it.
Many of those youtubers build only practical factories where looks and realism is not looked after, yes maybe partially due to the need to build bigger and bigger and therefore that fps problem coming in. Now thats the other end of how im building mine. I only build to get enough of something and scale where needed as new things come. and then focus on making it all look realistic and good and as they chant at the FICSIT, efficient. Lately making everything as compact as possible whilst retaining the realistic looks.