One of the things that strikes me is that it is quite possible that seninjutsu is possibly not unique to naruto and jiraiya.
1. Seninjutsu requires a huge chakra so its quite possible that madara has the capability to use seninjutsu ( see how he blocked suigetsu's blade )
2. When jiraiya finishes teaching yahiko, konan and nagato shinobi techniques he remarks that nagato has mastered all the 6 types of chakra in just three years. correct me if i am wrong but there are only 5 types of chakra ie fire, water, earth , lightning and wind.so at the time it bugged me , but now since we have learned about seninjustsu , i feel that the 6th type is nature chakra.
so pein will probably have a huge chakra and therefore be able to use an enormous amount seninjustu (nature) chakra.
3. with regards to naruto , i feel that we have not seen the real naruto (obviously) because , if you remember when naruto was training using kagebunshin , trying to complete the rasenshuriken which he uses on kakuzu.
now during that fight when naruto screws up his first attempt , tenzou remarks to kakashi that we haven't seen the real naruto yet. to me this implies that naruto may have used kagebunshin training to learn a lot of other jutsu quickly and maybe learn to harness chakra types other than just wind type chakra which also boosts the number and types of techniques he can learn.
4. the kyubi and naruto is a little complicated as jiraiya said that naruto will absorb the chakra of the kyubi and that eventually the seal will fade away into nothingness. my idea is that naruto will fight pein and even with the seninjutsu boost will be loosing ( due to reasons given above) and at that point will be forced to open the seal with the key that jiraiya asked that frog to give him and commence an impromptu chakra absorption of the kyubi. the resulting increase in chakra ( once he has absorbed the kyubi's chakra ) will enable him to call on a massively increased amount of seninjutsu ( nature ) chakra which will enable him to fight pein equally and win.
This is my first thread people (hope its not too long) let me know what you think.