Does anyone else believe that G4 was originally supposed to end a lot earlier? Having come out of two very unpopular generations prior, G3.5 not even lasted half a decade. Perhaps around the end of season 3 was where they would have started work on G5 if it wasn’t for G4’s unanticipated popularity.
Probably. When FiM launched, I don’t think anyone was expecting it to become the moneymaker it became.
Speaking of season 3 – there was a trend, generally speaking, for animated shows to last for two full twenty-three-episode seasons and the a thirteen-episode half season before cancellation, and I don’t think it’s too unlikely that that was the original plan with FiM, before the Powers that Be evidently decided it was better to keep it running. This, I think, might explain some aspects of how “Magical Mystery Cure” was written and presented – at the time, there would probably have been a non-zero chance of FiM not getting renewed for a fourth season, but no certainty that it wouldn’t be, either. So, the episode likely ended up in the odd position of having to be written to be a decent finale if no renewal came, but leave enough threads open to lead into a new season if the show was renewed.