Its an easy enough concept to sprawl outwards in any direction. I'm still pretty sold on the basics as you've mentioned, head to head strategy game vs an AI. But to add a narrative for the single player I'd do a simple thing: Have you regularly meet with the head of the opposing MegaCorp.Oh-ho? I would love to hear more on this. Thus far I've pictured this as a head-to-head strategy game, with the option of playing against an AI opponent. How do you envision single player working?
There was this moment in a convention game where I was the head of a massive interstellar megacorp fending off a bunch of rivals. It was crazy, I was run off my feet with work, all the schemes and feuds and betrayals and everything. And then as I rushed from one meeting to the next I passed one of my rivals in the hall, a man who I had already set in motion plans to rob of everything he owned - and I felt a profound sense of kinship. He had the same haggard, over-busy expression I did, rushing to the next meeting just like I was.
So what I'd do to add life and character to what would otherwise be an ice cold strategy game about technology and espionage would just be to have every so often the game pause and go to a conversation with the mind behind the opposing force. Maybe he calls you up on the emergency nuclear hotline in the middle of the night and tells you they've lost a warhead, maybe it's an international trade summit and you get to exchange a few lines of dialogue before the photo op. These conversations have a few branching options, and there's an occasional moment to connect, but mostly it's dominated by circumstances. After all, these are the only two people in the world who truly understand the big picture.
These conversations are random and there's a big library of them so they don't double up. There's a tendency in strategy games against an AI to characterize it - I actually thanked my computer out loud when AI Russia unexpectedly bailed me out of a stupid war I'd foolishly bungled my way into - and in a 1v1 strategy game I want to explore that concept a little. I want to communicate hints of Mr. Johnson's (randomized) personality through these dialogue scenes, give players a chance to get some insight into the mind of their enemy.
Eventually, when the player is winning, Mr. Johnson might try appealing to them directly for clemency or mercy. A sincere gesture to help put the world back together or a cold and ruthless betrayal taking advantage of the player's foolish kindness? At the end of each game the player will have a story about who Mr. Johnson was as a person and what his relationship with the player's CEO was. I reckon I could pull that writing challenge off.