and that was my whole point, it isnt ppl like neji, hinata, sakura etc. that are doing the so called impossible things, it is strictly naruto that are doing them, like winning against neji or taming the kyubi, and that doesnt make the theme "making the impossible possible" as that wouldnt fit the manga since only 1 is capable of doing it, however it fits perfectly with the "next generation is stronger than the previous" as that is what naruto's class mates are striving for and are heading for.
and even if the manga has more running themes, "making the impossible possible" isnt one of them tbh. your example of with minato is a lot closer to the "next generation is stronger than the previous" theme if you think about and as for chouji i dont think that the ppl of his clan will need the red pill to get the butterfly wings, i think chouji's father was surprised that he achieved it so early which caused the reaction.
the dead demon seal is special because of the price you for using it. what would be the point of having a seal like the dead demon seal that makes the user sacrifice his life to use it, if some1 could just unseal it like it was a locked door. it would make the whole seal pointless and former users would have utterly wasted their life in order to use it. i dont think you quite understand just how special the dead demon seal actually is, it is the seal minato used and sacrificed his life for in order to use it and seal half the kyubi chakra inside naruto and to save the village, taking all that away would just make it an ordinary seal and honestly, it should never happen, it makes the seal that much more mysterious and unique, and being able to unseal it is just wrong.
not really, naruto understood the very basics of the seal because he actually had tried it before when jiraiya open the seal a little bit where naruto almost killed jiraiya, but naruto wouldnt be able to make the same kind of seal tho.