Would it be possible to add the feature that ground that was pathed slowly recovers back to grass?
It's lovely to see where the main routes are, but if they're permanent that's only half as nice : /

The intent is that the main routes get covered with concrete. Storing a list of all altered tiles ever makes for some very large save files.

It wouldn't have to be "forever", just until they recovered to their original state.
And doesn't the mod already track the usage of them to decide when to degrade them?
Can't that info be used for the reversal?

Tiles do "heal" back up to the point of their last change, at which point they're cleared from memory. This keeps the internal memory manageable. Having to remember their original state and healing them back up to that point could take dozens of hours and would bloat save files considerably.

Ok, that's a fair point.

A possible solution I'm looking into for this issue is to adapt the Fish and Wildlife mod (https://mods.factorio.com/mod/fws) to update tiles to be more green whenever a tree grows on them, rather than restoring their original state. It's not quite what you're looking for but it would come with far lower save file bloat as it would be more of an "undergrowth simulator" rather than trying to specifically restore paths.