spoiler How extensive is the 'friendship of magic'

[Jeremiah 1,586]

So after watching Rainbow Rocks i noticed that when they used there magic to defeat The Dazzlings, Sunset Shimmer added to the group rainbow and after that she gained a half pony form which begs the question how extensive is the 'friendship is magic' also at the end of the season 4 final he asks

Discord: Wait a minute, where's my throne?

Fluttershy: I don't think you're quite there yet.

Discord: [chuckles] Yes, well, I suppose not.

 

which begs the question how far extensive is the 'friendship of magic' ?? but i am just randomly theorizing here, so feel free to answer back