Or maybe as an option that can be changed at start? I'm using sep 2018 community map
https://www.reddit.com/r/factorio/comments/9c6j1e/factorio_monthly_community_map_september_2018/
... and it features a scenario that builds a huge vertical wall far out where eyes can't see.

I do not know game's internal mechanics yet or this AI so well. Is it an infinite loop that the aliens moving in area causes game to "hidden reveal" more zones for them and they'll keep expanding that 1 direction north and south away from player infinitely, just because there is wall to break?

I mean in normal conditions one would want to biters to attack something that "player built". He can't have built something in place he can't see.

That behavior sounds correct.

I haven't looked at the map, is the wall of the player's force or neutral?

If it is the players force, then yes the player "built" it as far as this mod is concerned.

At the moment, I feel like the check for if the sector is explored before a potential attack is both expansive and disruptive to the AI logic. Depending on the number of player forces and it also requires either checking the entities on a chunk for their force or storing additional information on every chuck generated for force visibility.

How would expansion work with unrevealed chunks?

How do i check force? It says "cannot be mined" when i try to dig them, and they don't show "last user" name in tooltip.

edit: Found it:
local WALL_FORCE = "player"

I have played the map for many tens of hours now, and they don't expand north/south directions at rate that would be worrying. If they do cause more map to be explored in that direction, very likely new nests are not revealed so near the wall.

Other than that, the enemies are a real threat still now that evolution has gone past 0.9. I think the only way to fight that kind of power is the forcefields mod, i need to put those down much more. They easily chew through 3 layers thick brick walls with laser turrets behind them. As a player they don't stand a chance against flamethrower and nukes. But it's very hard to expand towards them at all because anything i build gets destroyed, especially the railways and big power poles. They cut the power to my turrets and so the losses can skyrocket.