most of my all-time favorite rap albums are already 10-20 years old. if they haven't been dismissed now, I don't see them being dismissed in 20 more years. Especially given the state of the rap game.
You don't see it cause a kid bein' born right now ain't told you how outdated it is. It's gonna happen. Right now, a 10 year old likely has no clue who the fukk DMX is, or even Nas for that matter, because it's not someone who's been promoted heavily to their generation. If they know Snoop Dogg, it's not for the same reasons you and I know him. All that will be old and nonexistent to them, breh. The only way it isn't is if they hear it thru their parents, but then again, how many of us were listening to our parents' music?