In regards to all the rare techniques, the only ones that could Lightningbend were the Royal Family, who were all selfish assholes who wanted to keep it for themselves, couldn't do it, or didn't think it would be a good idea to give it to a warmongering nation. Toph is sensible, so she'd have taught Metalbending at the first oppurtunity.

Regarding the rare techniques becoming widespread, yeah it kinda bothers me too. Aren't they supposed to be really, really advanced techniques that only the creme de la creme of benders can do? In the original series only like 3-ish people could bend lightning, now every average joe can do it. Also doesn't lightning bending require absolute peace of mind? I highly doubt you could achieve that in a loud, hazy, smelly, dirty workplace like a plant that was portrayed. Whatever.

Also, regarding Ammon, maybe he was visited by spirits, it's possible. The face-stealer spirit could have taken his, that's why he has that mask. I highly doubt that this power of his is the real deal, though. Sure, it stops bending, but I have a feeling it's only temporary, or that it could affect you for the rest of your life but is curable. Either way, you know how these fanatics are always portrayed: Either delusional or completely lying or hypocritical. We'll see.

Aang was killed while in the Avatar state. Though he was revived perhaps the original death had caused a split in the avatar chain and Amon might have something to do with that similar to the split in the Zelda timeline and all.

Also Koh having something to do with it became a very popular theory.

There's a word of god somewhere around given in an interview that states Aang dieing in the avatar state didn't affect the Avatar cycle. It's expanded upon in the [canon] flash game where Aang had to re-connect with his past lives in order to restore the cycle. I'll see if I can find it.

it seems p much accepted within the community that amon isnt energy bending and is chi blocking in some way. personally i think that he might just be chi blocking them and then getting rid of them before they get their bending back to trick the audience into thinking that he can shut benders down for good. id rather this not be the case though, since itd be cool to have a villain with good intentions rather than someone whos just like DEATH AND DESTRUCTION >:DDDD

also is anyone else a little annoyed that fire benders are still being portrayed as the bad guys? both mako and amon were attacked by fire benders in their past (could these be related somehow?) and also the first bad guy to be "energy bended" on stage was a fire bender.

Zuko is still alive. He retired from being Fire Lord a few years ago and travels the world as an ambassador of peace. His daughter is Fire Lord now.

http://ireallylikemuffins.tumblr.com/post/21573233437/i-know-how-amon-works-guys

If this theory turns out true then Korra will most likely lose her bending in order to get her to want to work on the spiritual side of things in order to get her bending back (as much as I would hate for that to happen because what happened to that thug was pretty disturbing).

Zuko is still alive? Room for another war *nodnod*