I think the 4090 is going to age well, it could be another thorn in Nvidia's side. With AMD sitting out the high end next gen, Nvidia doesn't need to do much for next gen if it were not for the 4090 but due to the 4090 being so quick they have to least beat it.
If the 4090 didnt exist, Nvidia could just come out with a 5080 thats 20% faster than the 4080 and people will eat it up, but because of the 4090 they cant do that now if they want to make money.
If Nvidia does that anyway then they can't price up the 5080 or its sales will be cannibalised by second hand 4090 sales, which is exactly what happened with the rtx2000 series, where buyers rejected it and bought second hand 1080ti's instead