One Question That Needs Clearing Up...

[Christmas]

. Since Sin is an Aeon technically he could simply be "unsummoned" and sent back into the conciousness of the Fayth to Dream Zanarkand.

No. Sin is not an aeon. It is just a bunch of pyrefiles hold together by gravity spells.

Rikku
"Wait, gramps! Who's Yu Yevon?"
Mika
"He who _crafts_ the souls of the dead into unholy armor."
"An armor called Sin."
"Clad in it, Yu Yevon is invincible."

And also, we all know that even Sin is defeated by the final summoning, Yu Yevon will merge with the Final Aeon and created another Sin.

As I recall, Auron says "when Jecht touched Sin, he became real."

I imagine that's because of Yu-Yevon, just as how (SPOILER)the Fayth can make Tidus real at the end of X-2

I believed that the term "real" is enabling Jecht to get to the real world and enable Jecht to live like a real person just like how Tidus make contact with Sin in the begining.