I voted "sci-fi" because it's the closest. I'm generally in the camp that doesn't think it's still "D&D".
Keep the same six stats, XP chart, and proficiency bonus, as well as d20 for all pass/fail checks and the existence of AC and HP.
Alignment probably doesn't work.
Keep the concept of races, but human would probably be the only one that remained. Even then, lots of other systems have races, so that's not big deal.
Most of the skill list would change. As far as having skills, D&D is actually a bit of a laggard.
You've also got classes, but they really don't port to another genre. Maybe the Fighter and Rogue, but that's about it; and even those would probably need some changes.
Basically, you've got Chapters 7 and 9 that port -- around 20 pages, minus some pictures. Depending on how you define "D&D" and "the system", that might qualify. I guess that's enough to start building a generic system, but it's not quite there. The problem with class-based systems is that the class concepts are so core to the system, that replacing them wholesale effectively guts the system as such.
On the other hand, I suspect the unification of various capabilities (saves, skills, tools, attacks) into proficiencies means that it'd be easier than ever to convert D&D into a class-level, level-less system; that would be much easier to make generic. Of course, I'd contend that such a system is even less D&D than a Gamma World "5E" would be.