PART 1
Ember crunched loudly on the fourth, maybe fifth, of Twilight’s gem-made bowls. Spike is so panicked, that he can’t concentrate on how much was being eaten. Not only does he have to be a proper host for two special guests, he now has to deal with a very hungry dragon!
“So, this is something friends do?” Ember asked in between chomps, “I could get used to this. Good thing I skipped breakfast. The gems here are delicious!”
Starlight Glimmer decides to speak up. “Um… actually, that’s not food.”
Ember gives a sudden belch, followed by her stuffed belly giving a sudden growl. “Got anymore?”
How could she still be hungry? Spike thought to himself. He turns to Starlight and sheepishly shrugs, “Dragons love gems.”
Suddenly, several loud chomps catch their attention. They both turn and see Ember chewing up Twilight’s gem covered walls. Her belly has grown even larger, hanging low as she continues to stuff herself.
Starlight turns back to Spike, “Fine, but you’re telling Twilight what happened to her wall.”
Part 2: >>1520610
No, it just wouldn’t fit into the canon.
Tartarus yeah!
If the show even mentioned that they’re carnivores, I certainly don’t remember it. Personally, I think their diet would be mostly fruits, vegetables, and bugs, just like real-life lizards. And like you said, gems and emeralds are like sugary treats to them.
My headcanon is that certain rocks and crystals are like candy, and to a dragon the castle is essentially the equivalent of a life-sized gingerbread house. Dragons do hunt for prey, but usually speaking animals are off the menu.
Spike should lay off the emeralds. Living on junk food is a bad idea.