As a league winning strategy Fergie's rotation was all but perfect, as the evidence shows: He had it down to an art. Moyes would do well to learn as much as he can from the great man when it comes to rotation.
But Moyes isn't Fergie - that's one thing. And what type of player is Kagawa capable of being for us? That's another thing. Is it possible that we need to make him just about the main man (the one who dictates play and sees a lot of the ball all the time) in order for him to perform to the best of his abilities? It's a concern, I must admit. Ideally he should be able to combine with - and interchange positions with - Rooney, but how this pans out in practice is impossible to tell before we've seen them in a run of matches. If it turns out that the two of them don't work well together, we have a bit of a problem on our hands: If, essentially, they're rivals for one spot in our best XI and do not combine well enough to justify starting them both, one of them looks more than likely to end up unhappy.
I was pleased that Rooney stayed on. But a lot of that has to do with the fact that Chelsea emerged as his only realistic destination. I think we would've been mad to ship him down there. But part of me thinks it might have made life easier for Moyes if he had buggered off - to some continental side: It would've made Kagawa the obvious choice in the No 10 role. A gamble, certainly, as we still don't know if Kagawa can become as good for us as he was for Dortmund - but perhaps a gamble worth going for. Worst case scenario: Rooney has a mediocre season, goes to Chelsea (or somewhere else, for that matter) come summer. In the meantime Kagawa still hasn't managed to establish himself, due to a shortage of minutes in his best position, and has become positively unsettled. Klopp begins tapping him up (he has said more than once that Kagawa would be very welcome should he want to return)...and there you go.
On the other hand, the best case scenario is that Kagawa and Rooney (and Nani or Welbeck) hit it off in style sooner rather than later, and become an incredible, interchanging force behind RVP...