Parmandur
Book-Friend, he/him
I mean, I'm not sure about the last assertion at all. As to the rest...new Classes and skills don't seem necessary, nor much in the way of new Weapons or Armor past what's in the DMG, even. The tech stuff can be handled fairly low key, and probably with much less page space than the Piety stuff in Theros.Depends on the direction you go.
You have Armor. Weapons. New Skills. Tools. Class changes. Maybe new classes. Probably changes to shooting. Probably vehicles. A lot of tech stuff depending on how you go like internet, hacking, phones, TV, recording, biotech, engineering, etc.
Painting the PHB in neon, chrome, and Japanese likely would get poor reviews.