We need a system in the cockpit that DEFINITELY leaves a crew with a basic flying panel, albeit limited - maybe no IAS or altitude, but at least power and attitude and does not just dump a pile of hot poop in the crews' laps and go off shrugging its shoulders. If that means a simple, battery powered AI, then fit it
Perhaps we should turn the question around and ask what aircraft does NOT provide this information. I know on the A320 you will always have at least a PFD and an N1 indication.