I think that makes a lot of sense. Keep the workout changing, keep it interesting. Why stick to the same thing all the time?

You will work different muscles (or the same ones but work them differently) if you switch around like that and I think that you would get more benefit by doing it that way.

But I do think you should pick a totally different type of excercise about 4 weeks into the program to really keep things shook up.

The main idea is to keep your body guessing. The more it is kept guessing the less chance it has to reach a stalemate.