Any reason not to put a structured wiring enclosure directly next to the house main breaker box?
Wire access space. When you plant something near the breaker box, you can't then enter the breaker box from the area blocked by that something.
You are going to be blocking off (what sounds like) a whole side of your breaker box from access. That can come back to bite when you need to add something later, and really wish that the other box was in the next stud bay leaving an open stud bay, rather than sharing a stud with the electrical box.