I liked the movie, but it wasn't as good as I'd hoped. Alicorns are supposed to live eternally, so what happened to Twilight? Where'd Discord go? Questions go unanswered, which causes me to not like the movie as much. It was still good, though.
Alicorns don't live eternally, only for about 10,000 years. I don't know what about draconequuses but I think they don't live eternally either. So for me the plot of MLP G5 could be set in far far future or it's even more complicated if you want to hold the plot of G4.
ClownfishTV covered the synopsis for the G5 movie. Sorry to say it, but if you want quality storytelling, it's not there. This brand's going downhill like everything else.
I don't think it will be enough to kill the fandom though.
Don't worry about the fandom princess, it never dies it just sleeps for a while until it's the right time to wake up. They might not be as big as their salad days but pretty much all fandoms are still alive and flourishing as long as there are still fans if you know where to look. And there are always fans.
G4 MLP was an anomaly compared to most of the generations in MLP. It was so good that it set the bar super high for an MLP series to be considered great. I don't think G5 MLP will be able to match the awesomeness of G4 MLP, but I'm hoping it'll be a good generation that bronies can enjoy.
[Grab Twilight Sparkle to calm her down] Okay, she's just happy that this world has gotten a lot of... love, a lot more than expected. Kid's gotten into a panic attack, because she's worry about the past repeating itself. You should "thank" the white alicorn with with the red mane, she bit off more than she can chew in showing her passion. You do you, newcomer!