Window frames should allow any tab on any edge, because it's a useful method of organizing the tabs!
You should be able to easily drag any tab to the top, bottom, left, or right edge of the window, and pop up pie menus on the tab to perform window management (and custom) commands on the tab or all tabs on the same edge, including covered-up windows.
For example: Lots of "todo" tabs on the left, "done" tabs on the right, a few "in progress" tabs along the top, "problem"
tabs along the bottom, so you can drag tabs between "todo" to "in progress", "problem", or "done", or select "close all left tabs" from a pie menu to clear out the "done" tasks, to easily manage your tasks with tabs.
You could even partition edges into different groups of tabs, if you wanted. And manage multiple tiled windows inside the frame. A pie menu on the tab will let you open it up to full frame, split to bottom, split to top (with the obvious directions).
Any sub-dialogs a window opens up could have their tabs laid out in a stack along a certain edge from a certain corner.
You could designate edges (or sections of adjacent edges corresponding to tiled windows) to show the tabs of sub-windows of the selected window (to implement tree browsers).
The app or document in the frame should be able to export custom commands that appear on the tab pie menu, so you can do stuff with the window without bringing it to the top or disturbing the currently displayed windows.
The point is that the user should be able to decide what tabs to put where for what reason, not that one edge is the right edge and all other edges or wrong, or using more than one edge at a time is wrong.