Are you on the latest version? I can rearrange them on mine. If click on "manage containers" there is a gray on gray bar on the right. If you hover it, your cursor should change to an arrow to rearrange them.
That allows for visual rearrangement of that particular menu, but as far as I can tell the new tab button's list does not change and the extension keyboard shortcuts are still limited to the first 10 containers, which are bound by their creation order.
A non-sanctioned way to mitigate this might be achieved by editing containers.json, but I'm wary of inviting sync shenanigans.
A non-sanctioned way to mitigate this might be achieved by editing containers.json, but I'm wary of inviting sync shenanigans.