Sometimes I need to use an US keyboard with dead keys, sometimes the normal variation. However, both layouts use the "us" map, so the tray indicator icon just displays "us" for both, making it difficult to see which one is active. If the user has added multiple layouts using the same map, the icon should display some information about the variation, or at the very least a number, such as "us1", "us2", to make it easier to see which variation is currently active.
In System Settings → Input Devices → Keyboard → Layouts you can setup a custom label for your layout which is then shown in the tray icon, if you configure it to show the label instead of just the flag.
Ah, true. The interface is not very discoverable: there is nothing suggesting you can click on a cell to change the value of the label.
The UI has since been changed such that this is obvious now!