My opinion is WotC has got plans about a d20 Modern 2.0. but it needs a lot of work for playtesint to find the right balance of power with the firearms and high-tech. How to explain it better? Usually with gunpowder the PCs can use guns but nobody has thought about when PCs are from a lower technologic level. Do you remember the Jakandor mini-setting? Now let's imagine being invaded by steampunk mechas. Neither Conan nor Tarzan can face Flash Gordon or Buck Rogers with a ray gun. Somebody will want to play superheroes, but the last D&D edition isn't ready for an event as skrull secret invasion, or an survival horror game when PCs are ordinary civilians and they face superheroes turned monsters (DC Darkest Night, Marvel Zombies, DCeseaded, Leaving Megalopolis, Super Zombies).
I call it "Cobretti effect" when PCs without enough weapons can't face enemies. In Sylvester Stallone's movie "Cobra" Bridgitte Nielsen's character couldn't face night stalker and she had to hide and run away like in a survival horror, but in the final fight Cobretti with enough ammo could be a true one-man-army to kill all the members of the New Dawn Cult, like in a classic shooter arcade.
Have you played Fortnite: Save the world? Do guess what happen when you have spent all the ammo and you have to face horde of husks hand-to-hand, without a ninja class with the right combo. Or you play with the ninja and a right combo and when you want to save ammo for the next missions you are attacked by husks with ranged attack.
You can play Street Fighters d20 or Overwatch d20 but both groups of characters can't be in the same game. Martial artist can't survive omnic crisis with only their fists. You can create a d20 version of the characters from Mortal Kombat, but these can't face demons from "Doom Eternal" without heavy weapons.
How is the XP reward when you can kill an elephant (or a dinosaur) with only a shot, or to drive a truck or an armored vehicle to run over a horde of zombies?