I might sound completely insane for saying this but regarding the modernization of the Mandarin without going to stereotypical comic book "Fing Fang Foom" approach, if I was Marvel I would take some inspiration from Hiromu Arakawa's Fullmetal Alchemist
. More specifically from its main antagonist, Father/"Dwarf in a Flask".
For those who don't know what I'm talking about, I'll leave a link to his wiki page which describes the basics:
To highlight a few points:
-Something akin to the Philosopher's Stone can be a good substitute for the alien rings. It would explain the Mandarin's similar powers plus his similar immortality.
-It also has its roots in science and more specifically, eastern science. Thus it plays thematically into the Iron Man tone without going "Thor" on it.
-It could maybe potentially tie into the Infinity Gems.
I don't mean to say IM4 should copy FMA. But taking just a bit of inspiration wouldn't hurt IMO.
Then again, maybe I'm going insane. I literally just came up with this on the spot. I haven't fully thought it out yet.