Oh, I know how strategic MP, tactical SP could work: co-op only. If you had 4 players online taking on AI, fog of war (including not seeing each other's every move), now that would be interesting. And that would be enough to say you have MP. Next step up would be to allow for all humans to take their turns in parallel--also interesting, but the developer would have a lot of multi-threaded race conditions to work through. And vice-versa: if the AI attacks multiple humans on its turn, allow for the humans to play tactical defense in parallel. I think that would actually be very cool, personally. I'd sign up online for that. Best part is, once you're set up to run 4 humans in co-op, you could probably scale it to 20 humans and higher.
Also, you're going to have to make sure the AI can use everything Derek put into the game. A feature isn't good unless the AI can use it, in a game with no MP. I don't want to have to throw half the game away to have the AI be competitive.
This is another case of scalability. You should be able to add features that the AI can scale to account for. For example, if all you did was add a bunch of units with lots of different attack/defense values, your AI should be generic enough to handle any N unit types with Attack X and Defense Y. In that regard the AI can actually be potentially better as you scale up, because the computer can track all the different possibilities better than a human can.