except not so pure and simple, there's no evidence that this was a unilateral decision by solely Hasbro. Honestly the whole finale smacked of being a potential series finale with the whole montage at the end, and given how the episode was said by the writers to have been written back in 2011 it's much more likely that this thing was written as a potential end to the series itself, since back then the shortened season would have put them at the magical 65 episode syndication mark that has killed so many kid's shows in the past. When it was written there was probably much more uncertainty over whether or not there would even be a season 4, maybe a direct to T.V. movie at a later date or maybe corporate was debating having the equestria girls spinoff be the new direction while axing the original series.

Honestly, a lot of season 3 came off like the writers were trying to wrap things up with a couple of vague outs in case season 4 became a reality, the trixie and discord episode, scootaloo finally getting an episode, and rainbow dash finally making it into the wonderbolts academy.

Actually especially the wonderbolts academy the original ending to that episode very much came off like an attempt to wrap up dash's ambitions by having her choose her friends and morals over her ambition. The current ending leaves things much more open for future development and could have changed after season 4 was actually confirmed.

But eh whatever, it's all speculation, I just highly doubt the alicorn Twilight decision was solely a Hasbro thing.