This is a hard tug between what my own childhood nostalgia says and an awareness of how the world has changed.
The line would definitely have variety attached. I don't know whether I would want a TV series as such with a 'core cast'. But I think it would be cute if each package had a QR code to access an online animated short for the character just purchased. Ponies should be brushable, irrespective of gender, and should come with a brush and a ribbon. Sorry, that's base line for me
I would obviously like a style of pony closer to G1, but it doesn't have to emulate G1 exactly. Just better proportions and a more appealing countenance than "I hit my face on a door" (G5).
I'd also like to see variety of species. So maybe adults, maybe babies, but not just earth, unicorn, pegasus. I don't want detachable wings, they should be part of the pony *lol*. That said, I'm not against a 'fairy' type species with changeable wings.
I'd probably begin with 2 earth, 2 pegasus, 2 unicorn and then expand each line out. Maybe repeating a character here and there but only to overlap one release (like we see with Cherries Jubilee/So Soft Cherries Jubilee) and then a new one.
Lots of colours. No dark pink packaging. I think lighter colours - white, blue, etc - present the colours better.
As for the world.
Years ago I wrote a backstory for the history of ponyland *lol* probably inspired by Mimic's episode and the 'first unicorn' mythology. I like the idea of a fantasy type world rather than slice of life. I like them each having their own magic irrespective of their species, and also their symbols don't have to reflect their fate. I dislike those concepts.
I don't really like how the G1 animation strips the earth ponies of the magic on their backcard stories. It's one of my main bugbears with the show, compared to the comic.
Comics? Yes, but I think having a digital option as well would be good.
Blind bags? Possibly. I'm thinking for friends/pets/etc rather than actual ponies, though. I don't need ponyland to be only ponies, but no humans unless fantasy related (witches, wizards, merpeople, ok - people being flown over from our world, not ok! LOL)
But having said all of that, if a series was going to happen, it would be fun to have a pony from "modern day no magic world" fall through a mirror (an archaic magic mirror in an abandoned castle, perhaps?) and end up in 'the past' pony realm.
I don't want to reprise anything from G1. But I don't see why a future generation couldn't start after G1 and go back to a world before it. Or a world between MLP Friends and Tales.
I just came up with all of that on the spot so if it doesn't make sense, I apologise xD.