Typical middlegame training

I believe the way the openings are studied doesn't really help a chess player once the memorized sequence of moves ends. I believe the idea to explore middlegames on specific openings could help to play better the openings one wants to play.

Totally agree. Openings just help prepare the castle for battle but the middlegame is where the actual attack begins. I remember playing a game with a peer and the openings led to a well-set structure of pieces on the board. But around the middlegame period, the attack began and it felt like the pieces fought each other to death (transferred out of the board). The feeling was amazing

The point appears to be valid. But think of it like this way that the opening guides you through the very first steps only just like in life, infants need a little support. Then, every one is on his/her own to choose the next path. And, with numerous paths to choose from, you can explore the next moves on your own instead of just following a set list of moves.

All good openings seem to have a general plan for next steps, but a lot will depend on what your opponent is doing, which is why middlegame is more about themes / patterns.