Sims are so good these days that it's difficult to imagine much of an improvement in the near future.
The feature that I would like to see is an easy way to tell which way I am (not the model) facing on the flightline.
Now I know that some have had a stab at this but I think that something similar to an artificial horizon (but showing where the CENTRE of the flightline is) is needed. I mean some sort of reference point between my current viewpoint and the central viewpoint.