If you like costly surprises during a remodeling project, then mechanical planning is not important at all. However, If you like your project to stay on budget, then a thorough study of the existing house is critical. By thorough, I mean understanding what's behind the walls, and the destination. This information is typically documented in "as-built drawings".
By knowing the guts of the house, we can properly design, budget, and execute a plan to its full intention.
How do you remove a structure wall full of mechanical ducts? Well, the structural part is pretty straight forward. However, the mechanical part is more nuanced. Our goal is to open up the space between the rooms, and maintain all of the existing room locations on the second floor. The duct work will still need to travel up, and they still need space to do so.
Our solution is to "thicken" the wall to create the needed travel space, and the width of the opening is 100% determined by the space we need for the mechanical. Viola!