I saw a post about playing from the losing side of a battle and thought that it would be cool to have the same campaign mission where you could play as either side. It would be interesting to hear the story behind what motivated each side to engage in battle and the challenges each side had to overcome outside of combat. This could add to the humanizing history element.
that doesnt sound as a bad idea on paper, but for an historic RTS like this, it might not be the best approach.
You would be changing the history -the narration too-. On a fantasy RTS game like Total Annihilation or Command & Conquer, you have separate campaigns for each faction and that’s good, imho.
The most important advantage I can find is the fact that you could recycle campaign scenarios that way.
What I think could be a good idea from your post is to create a “Change history forever” option, where the player would have the most challenging scenarios ever made in the series, and only the likes of TheViper could beat those.