If Kimmimaru were to be resurrected, full strength and all, it would be unfair.
He was so super powerful that it would just make the rest of the manga dumb.
They never really specify exactly how strong he was, but they did state he was far stronger than Sasuke, if that's the case, he could probably battle at a Hokage level.
Kimmimaru would most likely join Hawk [If he were to come back, for some reason] because of Juugo.
I don't know, I was sad that he got cut short because he was a pretty cool character with a lot of back story, but it would just be crazy if he came back.
Oh, and Kimmimaru wasn't part of the ''Sound 4'' He was just added last minute because Sasuke was in danger of being captured.