"So we should investigate first if we can change the code in a way that it can handle more than one Layout at a time. "
Please DO NOT let the search for the perfect improvement prevent you from implementing the adequate: Microsoft Word only shows one layout at a time. Many of the writers asking for this feature have said "copy the way Word's outline view works ... that's all we need." Those who use the feature heavily, like I do, are used to working in phases: the outline phase is where I arrange my topics and paste material into the appropriate topic. I flip back and forth from "outline" to "normal" during the writing and editing process, the switch to "Page Layout" for the final pretty-making changes.