The real "ageless" part of Hip Hop is storytelling, you can rap a story in the present tense and not have it be bogged down by all the previous shyt you ever rapped about in your life. Using your words, "imagination" is really the only limitation to telling a good story. However, rap fans rarely separate a rapper's persona from the stories they tell. Rappers aren't authors, they're not given carte blanche to juggle different universes, different genres, etc. The listener expects the cast of characters to more or less be the same.
Using your examples, Jay-Z and Nas are now looked at as Hip Hop moguls & 1%ers, the "evolution" of their content is largely that when they brag, their fans now see it as "goals". However, both of them have experienced difficulties catering to fans of their earliest material when that material was essentially written by a different person living a different life.
The commercial narrative about Nas's career shifted due to his individual success as an investor/businessman. On his last six albums, when he raps in first person and takes his listeners for a limo ride down memory lane past his earliest Hip Hop inspirations and revisiting old street shyt, the underlying fan sentiment he's fishing for is that he progressed from that. For whatever reason, Nas cares a lot about framing what his fanbase thinks about his newfound wealth and not wanting them to see a disconnect between that and the street oracle persona that inspired his first ten or so albums. He spends the majority of his new albums rapping in past tense, holding onto the past on some origin story shyt.
Nas's best songs in the last 10 years have all been pure storytelling tracks rapped in present tense. That being said, he himself usually limits his storytelling tracks to the street oracle variety.
Jay-Z raps predominantly in present tense on every album because his persona has more or less always been hustling for the sake of hustling. He can still hustle in a boardroom so there's no real disconnect in his content. However, he also hasn't dropped an album in seven years, possibly because he got tired of rapping about hustling and there isn't anywhere "grander" per se to rap about. Also, 90% of the time he raps addressing "you", e.g. the listener who covets what he has. Jay-Z is not a "look in the mirror" type of rapper and he doesn't have any real type of point to make either.
Quoting what I said earlier in the thread, most rap music is caught up in making a point to someone, proving someone wrong, in response to someone else's bullshyt or trying to win someone over... 90% of the time, the energy behind a rap track is directed at someone. Rappers who obsess over what their fans think about them will always have someone to rap for. Rappers who chase p*ssy like their life depended on it will always have someone to rap for. Rappers who care about maintaining a street persona will always have someone to rap for.
A rapper who is happily married, despises fame, doesn't maintain a street rep, isn't being targeted by anyone in particular and isn't running for political office isn't necessarily gonna feel the same compulsion to rap for someone else. IMO when Andre 3000 says he doesn't know what to rap about, he means he doesn't know who he'd be rapping for. When you already made the point you wanted to make to your audience when & how you wanted to make it, either you're gonna have to repeat yourself or you have to find a new point to make.
A lot of fans would be more than happy for him to repeat himself for an album or five, but if he truly despises what comes with fame then that isn't enough motivation for him to put himself out there again like that unless he really had some shyt to get off his chest.
I just know he’s an icon for his generation
