I'm currently pretty swamped with some Windows 8 work, but I do plan on coming back and updating the app bar. Can't give a date though. Would you like to contribute to the project?
The existing issues all have some workarounds. You can react to the selected Panorama/Pivot item in the view model and update the bound lists of buttons/menu items and the app bar will display whatever you have in these.
Make sure to vote on the issue - I will surely focus on it more if I see many votes.
Meanwhile - have you tried Windows 8 yet?
I have been focusing on this: bit.ly/WinRTXamlToolkit