Having gone over the leaked stuff (not including the unfinished episodes), I'm actually pretty optimistic. Nine seasons is a loooooong time for a show to be on, especially a childrens' cartoon, and it's pretty clear by now that the show is running out of stuff to do with these characters as they are.
Like, how many times have we seen "X learns a lesson we thought they've known since season 2" in an episode? That's more or less what happens when something like this lasts so long – the characters finish evolving and solve their lingering problems. Dash joins the Wonderbolts, Shy learns to be assertive, Twi evolves from friendship student to friendship teacher. And while adding Starlight, I think, has been good for the show and for evolving everyone else's motivations, it has come at the cost of deemphasizing elements that in earlier seasons were core parts of the premise. I mean, the whole point of the "friendship problems" table is to make episodes about solving someone else's character problem, since the mane six no longer had many problems of their own to solve. The premise has started to decay, and so the show is losing its direction.
A reboot fixes a lot of these issues, especially since it looks like most of the characters are staying close to how they are. A new version of, say, Fluttershy can take her base character and give it new flaws and insecurities that she can evolve around. For instance, instead of making her problem assertiveness, they could give her a goal like Dash had – to join some group, or start a wildlife sanctuary, or something like that. In fact, I'm surprised they never gave her a more "big picture" motivation in all this time, since it would have solved a lot of the staleness issues with her stories. The leaks seem to show them doing that with Twi in S8, which I think is a good decision. Interesting characters need to want things, since desire gives them an excuse to exert agency over the story. Without desire, characters become passive, and therefore boring.
I also hope they take this as an opportunity to bring a more coherent "big picture" perspective than they had in G4. It's pretty clear, I think, that Faust leaving after S2 hurt the show by depriving it of a central vision. She had a world and a trajectory in her head that was abandoned when she left and not replaced with anything better. While the writers tried their best, a lot of the issues with things like Twi getting wings I think can be chalked up to a lack of wider perspective on the general plot – had it been in the cards from the beginning, it would have been handled better. A related issue is that the show was never intended to go for nine seasons, which I think is why S3 was short (it would have been the last one had it not blown up). Now they have the luxury of knowing, from the get-go, that this series will be a channel flagship that will last for a long time, and so they can plan accordingly.
So anyway, the Tl;Dr: G5 looks similar enough to G4 (and has enough of the same writers) that there's a good chance that it will retain what we all still like about the series while also fixing some of its weaknesses. We all knew that the end would come eventually, and if it has to happen then it is best that it happens like this. G5 could well end up being better than G4 if all goes well, and if nothing else it will at least be new. The fandom can just pick up where it left off.