(This is an extension to ideas which partially have been discussed.
Allow to have the list view as part of the form view (and the other way around?)
We would not have to switch layouts to move from detail to list view, or vice verse which often makes no sense.
Well, why should use and possibly waste our time developing master-detail views where on the left (or right, upper, lower) side we find a portal listing the found set of records, and in the right pane the details are managed. Moving within the list, we also move to the associated detail. Moving from detail to detail, we also move in the list. Both are synchronous.
Currently many of us try to have this accomplished using a static dividing line and using a portal, or popover, or similar.
But it would be much more convenient - as this is a very general use case - if modification of at least the form view would be allowed adding a list view pane to the left or right. This would allow us to include a vertical pane with all those records listed automatically filling the space of such pane completely and being fully user modifiable.
Divider / Splitter Bar
Of course there must be a splitter bar (discussed elsewhere) diving both panes, and ideally it would be resizeable. The position of the bar could be fixed, or be sizable. Styles would apply as other common properties.
This means the functionality of the current list view will be combined with the functionality of the form view in one layout window.
I am not talking of a portal to be used here. It should really be the list view together with the form view.