I am most definitely NOT saying that a sharingan can copy a bloodline limit, i merely stated that it IS a bloodline limit. you are correct that a sharingan can't copy a bloodline limit jutsu, and yes Izanami IS a bloodline limit jutsu, but that would be FROM THE SAME bloodline limit that sasuke has, plus it's literally from the same eyes that performed the jutsu. You're right though, Sasuke could not copy Haku's ice mirrors, or Mei's lava style.
As for perfect jinchuuriki, Juubito is NOT a perfect jinchuuriki. he is being controlled by the Juubi, who doesn't even know who Obito is. plus, it's not even the complete Juubi seeing as it only has parts of Gyuuki and Kurama.
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yes, he will lose an eye, and a pricey one at that. he's also going up against an opponent that's stronger than the first Hokage. Seems like a good time to pull out all the stops.
I'd like to add, that no, a sharingan cannot copy other distinctive doujutsus like Obito's Kamui or Shisui's Kotoamatsukami, but Izanami and Izanagi were created by the Uchiha clan as a way of keeping prideful Uchiha in check. Multiple Uchiha were able to use those techniques, and even Danzo was able to use it (Izanagi that is, with aide of Senju DNA). So it's really only a bloodline limit jutsu in that you need a sharingan to perform it. Regardless, with so many that have already been able to use it, I stick by my previous argument that he probably already knows both of them.