Well you must live under a rock because they have done it many times with d20 modern and Cthulhu d20 old gamma world alternity, star frontiers, so you comment is invalid, move along .
A rather comfortable well-informed rock, as a matter of fact. Thanks.
My comment is no more "invalid" than your own. Let me try to clarify.
Nothing you site here is "D&D". You can use the d20
system -the mechanics, the [bulk of] rules- and lay
any kind of game genre/flavor trappings on it you want. That is not using D&D to make a "non-fantasy" D&D. It's just creating a different game.
If your query is intended to be "What would you like to see with a system where you make a character with these 6 abilities. Pick from a list of races/species. Pick from a list of classes/occupations. Pick from a list of [broad stroke] backgrounds. Now, go interact with the world using these mechanics for combat and these mechanics for non-combat challenges", then that's kinda meaningless. You can do that with literally
any and every scenario or genre anyone can think of, "Rural High School Cafeteria: the RPG", "d20 Mega Multi-national Corporation."
Unless I am misunderstanding, you are asking what people want to see as a supplemental "non-fantasy genre" book...somehow simultaneously,
for D&D. "Here's this book,
D&D 5e: Modern. Take it and "play D&D" with a party of russian physicists, japanese hackers and american doctors with guns, modern medicines, laptops and helicopters. Or apply any of these elements to your traditional D&D campaign [Your gnome druid finds an iPad in the dragon's hoard. The party runs across an interdimensional portal and out comes a tank flanked by iraqi commandos.]. It's super easy to do cuz it's made from/for 5e and just tacks on...like Legoes."
There will almost certainly be a "optional firearms module" in the DMG [to which I am also opposed, but that's a whole 'nother thread]. Think we kinda already know that. We know there will be other "optional modules" for various "
styles" of play. But separate
genres of play, basically, to tack on to D&D...no thank you. That's what games that
aren't D&D are for.
D&D 5e does not need to do that. D&D 5e is good at what it does, a broad range of possible
Fantasy [note the cap "F"]. WotC is welcome to try making new/
other games of any genre they like. But they don't have to [nor should, imho] be considered nor direct copies of D&D.
hmmm...not sure if that clarifies so much as makes the waters more akin to solid loamy ground.
Bottom line: Some people will, undoubtedly, want this kinda thing. Some [I hope "more/most"] people won't.