Planning main bathroom with pre-wall installation

A professional bathroom has no pointless projections for me.

The new era of the Energy Saving Ordinance / Controlled Ventilation in Living Spaces has not yet become second nature in building culture, i.e. from no longer chasing grooves into exterior walls for raw pipe stuff (and from raw pipe stuff that was unknown before) result "runs on the wall," which one tries to "conceal" according to equipment classes – often in drywall. On the other hand, you cannot tell from the boxed-in areas which were born from this banal circumstance and which are "intentional."

no pointless projections.

When I think of your zigzag wall, that’s already being measured with double standards, isn’t it?

I would still be much more annoyed by the chimney in the middle of the bedroom. But that’s old news.
I’m also in favor of option 4 with imagined wooden shelves extending into the slope.

Off-topic:
By the way, we have now found a great solution for the chimney in the bedroom, which means almost no space is lost:
we simply extend the wall in the opposite room right up to the chimney, so that a built-in cabinet/shelf is created in that room. Thus, only the small area between the chimney and the hallway wall is "lost." And next to the chimney in the bedroom, there is still a sufficient niche. There we will place a custom-made bedroom wardrobe.
Attached is a sketch of how it will look. I really like the solution.

The new era of the Energy Saving Ordinance / controlled residential ventilation has not yet become second nature in building culture, i.e. from no longer chasing exterior walls for rough piping (and from rough piping that was previously unknown) follow runs "on the wall" which are attempted to be "concealed" appropriately to the equipment classes – often in drywall. On the other hand, you cannot tell from the boxing which were born from this banal circumstance and which are "intentional."

You are probably right – in the end it might really look intentional, for example because of the built-in shelves.
But I do find it a pity that so little thought is given to this on the architects’ and planners’ side.
It would be best to integrate such pipes / exhaust flues into the exterior wall, ideally already during the masonry.

When I think of your zigzag wall, that is a bit measuring with two different scales, isn’t it?

Yes, I admit the zigzag wall is probably a bit exaggerated. It could have been done without it and it wouldn’t have looked worse either.
I hope it looks good in the end. Now I can’t go back anyway.
You will definitely get a photo when it’s finished.

Currently, our preferred solution is to move the entire gable wall forward to conceal the pipe boxes next to the washbasin and the exhaust pipe box flush, provided that this is feasible.
Below the window, we want to install built-in shelves and also a built-in trash bin.
Next to the toilet, we will also install built-in shelves somewhat higher up and a built-in brush and toilet paper dispenser further down.
This way, the pre-wall is optimally utilized and the built-in shelves will definitely look stylish.

Fireplace attached so that a built-in wardrobe/shelf is created in the room. Thus, only the small area between the fireplace and the hallway wall is "lost".

I would have swapped the children's room and bedroom and moved the entire wall as well as the door so that several meters of wardrobe space are available in the bedroom.

Currently, our preferred solution is to move the entire gable wall forward,...

How deep will the window sill be on the inside then?