The post-credits scene makes me think that the special might be about the earth ponies starting to feel inadequate compared to the unicorns and pegasi, and have them rediscover their own magic. I’m even thinking there’ll be a slight change to how it works so it’s more “noticeable” than it was in G4.
If Argyle had found the “Journal of Friendship” book, it is possible that his research could provide important clues about magic - moreover, it will be interesting and not a little fun when the ponies learn how diverse and potential magic is for all three pony tribes. Zipp has a strained relationship with her sister who needs to get in shape when it comes to flying, and Sunny needs to research what she as an alicorn can do, with the help of Izzy, Hitch and Zipp. Also, Sunny can find more secrets in the special after her father, maybe the two special books from the G4?
If Sunny wants to find out what happened to Canterlot and Ponyville, an expedition to the valley could take place as soon as possible, as Zephyr Heights is now available for the Mane 5. We do not know what they’ll find, they will find one. intact but forgotten society, or ruins - or nothing? Sombra abducted the Crystal City with him when he died for the first time. But I do not think Twilight, who may have received predictions about what will happen, will hesitate to leave aids that can be of great help to the ponies in the future. As a library that can teach the ponies about their magic and history that had been lost.
We can find what happened when the magic disappeared, but I have a feeling that the final answer to this can wait throughout the G5 while world building, exploring and restoring Equestria occupy the adventures of the Mane 5. If it was a powerful enemy that was behind the attack, it is possible that the cause will not be explained as long as possible. So that Sunny could concentrate on spreading friendships, restoring the old contacts, learning about the world - the twelve states of Equestria can be the beginning - and creating alliances and friendships, in the face of mistrust, misunderstandings, hostility and cultural collision.
I think the G5 will not be about a series of separate adventures that completely replaced each other, but a continuous story from beginning to end, in contrast to the G4. The script behind the movie points to this.
And speaking of Netflix; Hasbro is not just anyone, Netflix can not provoke these unnecessarily, as seen in the case of the delayed first trailer. Netflix is dependent on the movie and TV producers.
The G5 has got a dream start that Hasbro had hoped for, now they can continue down the course which may have been decided already in 2019/2020 if the whole case around the IDW S10 has something to do with it. It is no coincidence that the various non-pony people were apparently exposed to the same thing as the Ponykind in the G5. There was a lot of uproar over Discord`s deception and the disappointment that Grogar was not “the End boss” of the G4. There was also, as seen in the escalation of the S10, a strong interest in building lore about people, about the world, about background etc.
If Grogar comes to the G5 … we are entering very interesting times for the coming years.