> If we don't want to use Wipfs, maybe we should at least have the player invest into some kind of robot that allows the lorry to work on its own?

Yes, the Guided Rail Lorry(tm) should be something available when developing your settlement further. Invest some resources on that and your automatic settlement is going, leave it alone and you're back to the hard way with no logistic.
The intelligence can derive from whatever. Robot or a sweet little wipf with a mining helmet

> What? I never said that.

Hm, yeah, got that wrong. He mentioned the super-flint thing.

> Why exactly do we need rails?

Yeah, it's also possible to have the landscape do the job. But I think rails are just easier to handle. You don't have to look after every hole you dig, not every meteorite destroys your whole infrastructure and it's not that easy for an enemy clonk with a shovel to cut your whole supplies.
As well, your lorry becomes a transportation system to overcome obstacles like lava lakes or just an abyss. Or you can let it drive above a lode of gold and have it drop the flints from there.

> Must not forget though that it should not give you protection from enemy attacks... Sooner or later tracks will be in a contested zone.

Yep, there are some vulnerabilities to think of. When attacking with clonk to clonk weapon (spear, bow, musket) the clonk(s) may fall out. It shoule be even possible to shoot while inside the lorry thus enforcing wildly firing lorry chases!
Another thing is the attack with explosives. Hit the lorry with a well targeted cannon shot in midair and it drops off the rail, spreading its contents everywhere.

> It would be unclear where exactly to search - unless we bind it to a base region or something.

You search for the nearest storage building which provides the needed material. With the 'might need' approach you still could end up with your material at the wrong place.

> Just have a storage in front of it that accepts all kinds of materials.

Okay, that makes everything easier.