I'm trying to imagine what Elon, as a visionary, thinks about the existence of speedo clusters.
How people who don't drive see instrument clusters:
They look awesome, lots of colors and gauges, Especially AUDI
What information is actually shown:
Information that is actually valuable and can be absorbed with a fraction of a second.
In case of huge, horizontally positioned LCD that is closer to drivers field of vision (left upper edge) than on Model S, I can't see technical reasons why Model 3 SHOULD have another display device (HUD/LCD) closer to the windshield. And the more autopilot advances, the less and less it is actually needed. There are some things that can and should be resolved, like blind spot warning. Either LED-s in the side mirrors or steering wheel vibration/torque + sound is enough for safety rating points.
I see no reason to display time, outside temperature, battery temperature, state of charge, gear selection, tire pressure, vehicles overall mileage, power/regen value, trip time, trip distance, average fuel economy, vehicles around etc EXTREMELY close to windshield. People spend more time looking at their smartphone screen rather than speed.
If HUD will be available, it will definitely be a Premium option. It will DEFINITELY not have another set of brains. Information can be mirrored directly from main screen in simplified form. I'm not even sure I want it. For 300€ yes definitely, for 1000€ no. But HUD requires special windshield option.
What the prototype had:
What is needed to make it legal:
I would only change PRND - absolutely pointless to show all possible values at the same time.
Also I would display P in place of speed if P is actually engaged.
What should driver do to be a better pilot (or copilot) look on the road! not RPM, battery temperature, range, miles driven, vehicle mileage, time, power output, ecometer/how many trees you've saved and all kind of utter garbage.
For random low priority information (windshield washer fluid low, tire pressure error etc) there is definitely no point to make another display near windshield/on windshield.
I would also add that upper edge of 15" LCD looks to be very close to windshield from eye level. Even closer than Model S speedo. The only difference is that it is reachable and that it can be seen not inside the steering wheel but rather above right hand which is on the steering wheel. Which allows Tesla to design more appropriate wheel