Just pondering this one, and while I am sure it would be outlawed in a flash, it would be road relevant...
How about if the HUD was not for instrument reading, but instead was fed with a radar image of the track in front of the car? That way, the drivers in spray could flick a switch and instantly get a view through the mist. Granted, they would still be grip limited, but they would be less likely to pile into one another, and they might even be able to overtake easier?
On the main question, I doubt that the weight issue would be significant. They've run with heaters on their visors, and I expect the smarts for a HUD would be lighter than that. They wouldn't even need a backlight as such, so could have LCD mounted directly in the plastic of the visor. That would be cool, if a little distracting for the drivers.
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