I always found frustrating, middlegame books shows examples about the different positional tools and imbalances like pawn structure, good or bad pieces, activity, weak and strong squares, space and development, but it was hard to use in my own games, because the examples were from diffirent openings. Example when I was a kid I never got positions with isolated pawns. I played a lot of sicilian defense games with both colours and played a lot of pawn storms, but hardly played with isolated pawns or I did not know much about space advantage.
My dream was a book where the different middlegame themes will be shown from games where the players played the lines which I also played in the sicilian defense.
And other books about all the different openings. So I can use much eaier the strategical tools in my own games.
I think there are already good books which use some of these ideas, like the Dutch Stonewall by Jacob Aagaard