The layout of current PFDs is historic, has evolved subtley over years from the basic T instrument layout devised by the RAF pre WW2 and is the de-facto display format. Changing it would require additional training and certification and would be considered as a heresy in some circles! The only changes which would possible in the short term are changes to the presentation and display of information.
However, this should not stop the system evolving. The modern PFD is a fussy, sometimes confusing and very fatigueing instrument to intepret. Fatigue of pilots is a safety factor which is going to be a bigger issue in the future, largely due to the improvement of safety in other areas and the increasing trend for airlines to treat Flight Time Limitations as guidlines for everyday use rather than limits for safety.
Having said that, here are a couple of my thoughts for what I would like to see in the future:
Having watched my kids playing a flying game on their games console, I've noticed that they prefer to fly the 'aircraft' using an outside view. In otherwords, they are viewing the aircraft from a position outside and behind so they can see what the aircraft is doing. Of course this enables them to watch cool thing happening like missiles firing, but having been allowed to have a go a couple of times, I also find it very easy to fly in this way. Accuracy would be compromised, but why not incorporate a Flight Path Vector system superimposed on the horizon as used in the Fly By Wire Airbus aircraft? Also, why have the height, speed, heading and VS information? If the aircraft is in some form of managed mode and you are within a few feet/knots/degrees, why not hide the information until certain parameters are exceeded. You would need some sort of trend vector such as the speed trend vector on a conventional PFD.
Also, why is the PFD stuck below the coming below the natural eye line? On the few occaisions I've flown with a HUD (Head Up Display) I've found it to be vastly superior to the conventional heads down dispays.
The main improvement could be with the Nav Display though. When the current crop of modern airliner instruments were certified, Pacman was the cutting edge of gaming technology and these displays are in the same league! You only have to look at what some of the modern business jets have to realise how things could improve in airlines. Things have got better with improvements such as vertical profiles on the NDs of the more modern Airbus FBW displays, but there is huge room for improvement. So, why not have a 3D nav display superimposed on the outside view of the PFD I described above?
This combination display would have an image of the aircraft superimposed on the real terrain on a head up display, maybe even the windsheild. It would have little quantative information, repalcing these with a flight path vector and trend vectors. It would have the navigation track superimposed and landing systems (such as ILS if it still exists) would be a cone you could fly down onto your superimposed runway giving you a very user freindly low vis system. The gear and flaps would appear on your aircraft image, so would airframe anti icing as your leading edges glow red.
The benefits of the above display would be more situational awareness, less pilot fatigue and shorter training times. Think 'outside the box' and play a few computer games!