While I fully expect automakers to play that game however they can, there's not a huge benefit to moving the display up into your field of view from just below it (like a Prius), and there are a number of downsides.
And a real HUD, beyond deciding what information to present and how to present it (as you rightly pointed out), is also technically far more complex than slapping a display on glass:
"I commented on the original post, but this is a great example of reason #1 why HUDs are still green after 50+ years.
Colors are additive with the outside world. There are conditions (sunset/sunrise) where you could get misleading information. Ambers and reds mean specific things. (https://images.app.goo.gl/G5Udbponiu1M1Fnc6)
"The optics in projecting an image reliably at optical infinity (makes it look like a billboard 500 yards in front of you rather than a TV screen 6 feet from you) are actually quite complicated and tuned to the specific wavelength. Having multiple colors drastically increases the complexity, or reduces the clarity because you have to compromise on the optimal wavelength.
"Generally the goal is to be as consistent with the head-down display as possible to limit the head cycles spent context switching, but in the case of colors we have other means of calling attention to important info: boxing and flashing both do a pretty effective job."
Anything less than that just risks becoming obscured, with less contrast and similar focal-distance issues than a good instrument cluster.
That said, I wouldn't mind something I could stick on the glass of a vintage vehicle up in the corner so I can add instrumentation without modifying the dash.
But you're still going to get a much better approach with a windshield-mounted glass combiner, Picture Generating Unit and a projector.
And a real HUD, beyond deciding what information to present and how to present it (as you rightly pointed out), is also technically far more complex than slapping a display on glass:
"I commented on the original post, but this is a great example of reason #1 why HUDs are still green after 50+ years. Colors are additive with the outside world. There are conditions (sunset/sunrise) where you could get misleading information. Ambers and reds mean specific things. (https://images.app.goo.gl/G5Udbponiu1M1Fnc6)
"The optics in projecting an image reliably at optical infinity (makes it look like a billboard 500 yards in front of you rather than a TV screen 6 feet from you) are actually quite complicated and tuned to the specific wavelength. Having multiple colors drastically increases the complexity, or reduces the clarity because you have to compromise on the optimal wavelength.
"Generally the goal is to be as consistent with the head-down display as possible to limit the head cycles spent context switching, but in the case of colors we have other means of calling attention to important info: boxing and flashing both do a pretty effective job."
https://www.reddit.com/r/hudporn/comments/i8fp9m/the_hudset_...
Anything less than that just risks becoming obscured, with less contrast and similar focal-distance issues than a good instrument cluster.
That said, I wouldn't mind something I could stick on the glass of a vintage vehicle up in the corner so I can add instrumentation without modifying the dash.
But you're still going to get a much better approach with a windshield-mounted glass combiner, Picture Generating Unit and a projector.