Hi Pablo,
yes I agree the current UI of Scribus is more like a maze - long ways of navigation, much scrolling and so on. My first idea was to stack single panels (separate or as group) in an icon bar. That means every panel has the full screen height (no more scrolling). But the Property Panel is another stack and you have to search again for features.
While I'm was working on a more detailed UI proposal I received many user feedback on different channels and the common points are:
- split PP in smaller pieces
- let the user decide the arrangement of single panels and most often features
- design the panels more space optimized (the other parts of ui too

).
The current state of my concept is not exactly brilliant. But can be upgraded after new insights

I see two extreme layout cases for the UI:
1. show most of the features on one screen (beginner and user they need quick access)
2. hide most of the features (professionels with full focus on document and shortcut user)
So we need:
- flexible panels and docking mechanic
- more shortcuts of important features
Furthermore I think clean up of panels, space optimization, new control elements are working perfect in both cases above and is necessary for a great user interface.
Your feedback support these new direction and I have to think about changes in the Indigo UI. Currently my focus is on the panel clean up and building new control elements... That's the first part of the Indigo Project.
it would be possible to activate more that one toolboxes one below another, right?
About your question, you can group more than one single panel in a panel group. Based on the single panel size you can see all panels in these group in one screen without switching to another icon tab. Every Panel group is stacked in the icon bar.
greets
Martin