With TiSDK 3.1, windows within a tabgroup are no longer heavyweight. So the menu should be associated with the tabgroup. That would lead someone to try:
But that fails with a build error. Or, you might try:
But that also fails. You must put the menu tags within the window tag inside one of the tabs.
A further consideration is that if developers want to have a different menu associated with each tab's window, they need to destroy, then re-create the menu on the tab change event. Being able to put the menu within the tab group within your index controller would let you keep this menu switching code in the index.js and not duplicate it across various subcontrollers.
May relate to https://jira.appcelerator.org/browse/ALOY-277