The cloud of bars
If you look at a reasonably complex page in edit mode in Magnolia 4, the sheer amount of edit bars and new paragraph bars can be overwhelming. Orientation becomes more and more difficult the more paragraphs you have and finding the edit bar of the paragraph you intend to edit can be somewhat challenging. Furthermore, the areas of the page defined by the web designer or information architect to structure its content are not visible or get lost behind the cloud of bars.
Collection paragraphs
Furthermore, problems arise with paragraphs mainly existing to host other paragraphs. These collection paragraphs - which usually have no or only few fields on their own - are visually not easily distinguishable from paragraphs with actual content. As a result, it is unclear that you first have to add a collection paragraph before you're able to add any sub paragraph, in particular if you're a new user or unfamiliar with the collection paragraph. It is often not obvious to you that you'll have to e.g. first add a news list collection paragraph before you can add a single news paragraph.
Scalability and visibility for actions and options
The edit bars currently offer only very limited space for buttons. For narrow paragraphs, a bar is hardly providing enough space to contain any buttons at all, let alone buttons requiring longer labels. In addition, there's a growing need for a location to put paragraphs options or the page as a whole. Examples of such options are a language selector for the currently shown page; information on the currently viewed version of the page; or even development data such as the name of template used to render the page.
A reworked page editing has to be able to host a larger number of actions, possibly provided by additional installed modules, and shall provide an equally extensible location for options.