everything is possible in objc!

https://gist.github.com/84ab564cf1ae26ce4ad100b103502b17

The tricky bit was figuring out that two methods seem to be required for switching a tab. One was discoverable via quering actionsForTarget_forControlEvent_(), with targets from .allTargets() and events from .allControlEvents() for the tabView. This returns a selector, whose name can be obtained from sel_getName.
The other I figured out mostly by guessing.

Attaching these methods to keyboard shortcuts is left as an exercise for the reader( mostly available already in the forums)