Well, Twilight runs Friendship Dictatorship until she didn't, which to be fair weren't for the very long. The ponies then returned to their natural order, three tribes. And maybe it was just me but they were perfectly fine without magic.
Um.. Princess Celestia feels like a safe answer, but I want to say Princess Twilight. That girl doesn't need a royal title or represent friendship or rule over a country.
Sunny Starscout is an alicorn of recycling garbage
Also the city had become littered with garbage for some reason.
The princess has declared the new holiday
I mean nanotechnology could be considered as a replacement for magic. Ponies who wouldn't know anything about the technology would certainly think they were doing magical miracles. Magic (nanotechnology) could be deactivated and reactivated at will and then do certain things when harmonised between the ponies that represent the elements of magic.