The canceled idea after the movie.
I'm just gonna get straight to the point, we need to make sure Hasbro listens to us and puts effort into G6. G6 being good is the only way to revive the franchise and make MLP relevant again.
I remember that G4 didn't exactly end on the greatest note. Most people agree that the show started to gradually drop in quality after maybe season 4 or 5, but it still had plenty of good things that kept it enjoyable. Objectively speaking, the show didn't become outright bad until season 8.
After the G4 movie, the quality of the writing took an absolute nosedive. Seasons 8, 9, and those weird season 10 comics had the most incomprehensible writing choices, and the majority of them felt like the first draft. That's not to say that the pre-season 8 era of the show was perfect, but if there's one thing that separated it from the post-movie era is this: the writing felt like they actually cared and tried. Even with the occasional bad or mid episode (which is normal for any cartoon show), you could tell that they actually cared about what they were writing and the audience's intelligence.
I don't know what was going on behind the scenes during the post-movie era, but considering that Hasbro had to scrap a bunch of their plans for expanding the franchise after the movie got a mediocre reception, I suspect that the stress of all that caused the writers to stop caring as much. Or maybe Hasbro screwed them over and wouldn't allow them to proofread their work, I really don't know.
(As a disclaimer, I'm not saying you're not allowed to like certain eras of the show, most of what I'm saying is just the majority of what I've heard from fans. Some people prefer the earlier seasons (1-3), some people prefer the middle seasons (4-7) some people may even prefer the post-movie era. Personally, I prefer seasons 1-7 and the movie, plus some of the comics. There are some post-movie episodes and ideas that I like though.)
Because G4 ended in kind of a lackluster way, people were cautiously optimistic for G5, hoping it would have the strengths and none of the weaknesses of G4. And, well… we all know how well that turned out.
Basically what I'm saying is that G4 ending in a lackluster way and G5 failing is all Hasbro's fault, and in order to fix what they caused they need to start listening to their fans for G6, and pick the best ideas.