I've never found a food that my dogs don't like yet, but they're all pretty much hoovers. For me the main con is transitioning from one brand to another, it takes a while and it means more containers open. I typically switch every 3-4 months.
Some (and again, none of this is meant to be a revelation, just an observation) dogs just have an iron stomach. So it seems like rotating food is working for them. Other dogs are much more fragile. What I have found is over feeding certain single protein can create a sensitivity.
The problem with rotating complicated commercial PF, is that so many recipes have so many ingredients, all those ingredients represent a lot of elements for a dog to digest, and then rotating them all around, increases that difficulty.
I really like the idea of food rotation to cover all the nutrition bases and keep my pup my pup from being bored with her meals. But I also fear my girl will have digestive issues and I won't be able to pinpoint the problem. My pup received one commercial, multi-protein puppy food, four different treats including freeze-dried liver, baked chicken, packaged treats and hot dogs. I sometimes top off her kibble with a bit of pumpkin, cottage cheese, cream cheese or peanut butter. Some days her stools are perfect. Other days they are too hard. Rarely are they too soft. I haven't been able to figure out what foods cause changes in her stools but then I've not been keeping track of what she's eating. I really like your idea of a food & poo journal. It should help me figure out what foods cause unacceptable changes in her elimination and might give me a foundation to build on as I attempt to introduce new foods (veggies, eggs, other commercial dog foods).I keep a Feeding Journal (including if and which supplements are used) and then what is the result of the stools.