This is where I start running out of answers of my own, but hopefully others will have more interesting... wait, I've thought of one!

That Fluttershy is employed to manage Ponyville's wildlife like Rainbow Dash was to manage her weather. And following on from that, that she's college-educated.

When we fail to love and tolerate, our greatest enemy is ourselves.

That the Sirens have been on earth for 2000 years, ruining things from the shadows, while their very presence polluted the world with magic, and that's why Humania is full of purple-skinned freaks.

Less headcanon and more of a whiny complaint, the default pony choices for TF2 crossovers feel very unoriginal to me.

7039663 The only reason Twilight was popular as The Sniper was because of "Does this count as camping", she would've been much better suited to The Medic or even The Engineer. At least I could kind of understand Applejack as The Engineer, they're both Southern.

7178923
I just got real tired of people using personality for role-matching, especially when it seemed nobody has tried using skills for role-matching. Honestly, she'd be a better heavy due to probably being the strongest, for example.

I try not to judge - or meddle with - other people's perspectives and worlds. There is such a vast richness of ideas out there, it's like an ocean. I don't mind contributing my droplet and be satisfied with that. I'd rather go for a swim.