I like to have nested portals of 1st-degree, that is a portal with a popover button and a another portal within the popover.
Advanced databases often contain more than two or three tables. The data relations are complex and to display them in a smart ui portals and popovers are a good solutions. But currently this is limited because you cannot show a portal inside a popover that is placed in a portal. Alternative solutions (workarounds) using popup menus, floating windows, global repeating fields, or faked portals have their limitations, add clutter to the layout, are complicate to setup, and/or increase the complexity of the program.
Because there cannot be more than one popover open at any time, this "portal inside portal" would be limited to 1st-degree. Still it would be much appreciated and very helpful for designing better user interfaces.