There are 2 modes proposed, one turn-based Grand Campaign and the other narrative.

Fundamentally, a campaign is a series of scenarios/maps that have to be played in sequence (i.e. once you win part 1 you will have access to part two etc.) and that build on each other. The storyline is ideally meant to be provide historical background. Unfortunately (or not) it is not possible to carry over results of the previous campaign scenario onto the next one, i.e. you start with a small army in game 1 and end up with a larger army, which n turn saves as the basic setting for game 2, etc. I believe the challenge would be to orchestrate dynamically allocated balancing from game to game.  

Being able to build roads as a start (without rails so far ) would be a nice new feature for 0AD as it is. Roads could increase movement speed of everyone (including your adversary) compared to moving through forest and grassland. Pathfinding is the main issue here unless the path is preferably following the road ( so nothing to be found). Pathfinding strategy could be to follow the shortest road through the system and only revert to the original pathfinding scheme at the end of that road.   Roads have been discussed few times already but we never progressed so far. As an example in this thread:  

There was a mod with an interesting campaign, but it needs to be updated to work with the latest version: https://wildfiregames.com/forum/topic/28303-campaign-macedonia-rise-to-power-balkan-campaign-into-asia/page/9/

The position of project leader is vacant for two years.