Bevendre

My mistake….

There is some evidence of this, partially in her coloration being nearly equidistant between Spitfire’s yellow and Soarin’s blue, but mostly in her attitude, drive and talent.  Lightning’s flying ability is prodigious, and if she were the daughter of two of Equestria’s most celebrated flyers then she would be considered a legacy, not uncommon with talent.  The desire to impress her mother, and father would explain her tendency to push herself further than any other, despite the risks, although this would depend in part upon her upbringing and relationship with her parents. 

   Not a popular fanon, or even one that I’d ever heard of.  Given the implied age difference between them (Spitfire and Soarin are both portrayed as being at least a few years older than Rainbow, who is roughly the same age as Lightning Dust) it is nigh impossible.
   That being said, it is possible.  Magic has been shown to allow for time travel, albeit with limitations.  If Soarin’ and Spitfire were the foals of Lightning Dust, and sent back in the short period that the time travel spell lasts, then it could work assuming that the spell could be severed by the one who cast it.

Sorry I can’t defend this one very well, I have never heard anything like this one. 

I’ve not seen or heard of any such blog, so I can’t speak about that.  As for the Canterlot Wedding, I think it was good.  It had a few flaws, namely the instant inclusion of Shining Armor and Cadence without lead up, and several points of Chrysalis’s plan which paint her as overly ambitious and prideful.
I didn’t mind the ending too much, because to an extent it makes sense.  The joining of Shining’s and Cadence’s magic to create the effect that it did is often panned for not making sense, but it does to a point.  The diet of changelings and windigoes prove that within MLP canon it is possible for emotion to be channeled as energy.  On top of that, it is shown several times that magic may be boosted under times of stress (Twilight), or under the influence of certain emotions (Sombra) both of which were factors during the occasion.
Shining Armor is shown to be an incredibly competent user of barrier magic, the very thing that cast the changelings out of Canterlot, and assuming that Cadence acted as a sort of amplifier for the reasons explained above, then the ending works very well. 

As far as I know, Applejack says that she won her hat at the fair, but not how she won it or from whom.  As such it is still possible that the hat is her fathers.
As for how I feel about it, I think it very likely and touching.  Applejack has been shown to be very attached to her hat, refusing to relinquish it when dressed formally.  This is distinctive of an emotional attachment, one that could very easily stem from memories of a lost loved one.  As has been shown in the Apple Family Reunion, and said by Faust, Applejack’s parents are dead, and this would establish such an intense attachment in Applejack to her hat.

I’ve not heard of this fanon idea, but I rather like it.  Assuming that the holes on a changeling’s leg are unique to the individual then having a locking system reliant upon turning a series of pegs in a pattern fitting the holes on a changeling’s leg, and dependent upon variable pressure could work.  The sequential locking system would be similar to the common setup of locks in which the tumblers are fit in place and opened by the teeth of a key, and a pressure system like that which exists in some safes to prevent them from being broken into.