Partial Fix Shift down has been implimented on the FeatherChorder, both USB & BLE. This chord send a shift down event until the next keyevent is sent, which means that shift is held down for any mouse events until the next chord is sent. This could be implimented for Alt and Control the same way if needed.
add the ability to have dedicated modifier keys (like a conventional shift or Control) that just send that code along to the host.