Lets face it, the game is entirely done in our freetime, and that is the limiting factor, for sure we can make a decent AI or optimize it to run on lower hardware. BUT as we have very limited amount of the human resources (time) available, we need to focus on the more important game elements, like the main features. So we need to make a tradeoff, and AI for MP is as low on the list as it gets.
And if we have to decide whether or not we are going to develop forever and finally drop our freetime-project unfinished or just do it to the point where the game is enjoyable in a feasible time and then keep on adding new elements and improving the game. I think it is clear what we'll choose.