1. Change container
This would allow me to change a tab's container without duplicating it.
2. Group tabs by container
Tabs would be rearranged, with all the tabs for each container grouped.
3. Delete all tabs in this container
This would operate on the current tab and close all tabs in its container.
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Not exactly what you asked for, but this might interest you:
Or maybe this (a bit less related to containers, but contains the same function as select-container-tabs and a bunch of other selection options too but is still a bit work in progress)
Once you have the tabs you want selected, you can use the built-in move, close methods.
Hope either helps (a little).