We will obviously get a new Mane 6, or even a few more or less characters. Given that names have been used before (G2 Sugar Belle and G1 Sunshimmer [Sunset Shimmer]) what about the new main characters are actually the next Gen of the prior?
Let's use Flurry Heart as a perfect example to lead the next generation and guardian of the elements of Harmony. This little rebellious and reckless Alicorn would make the perfect heroine to start. Let's then add the Cake siblings. We already know she doesn't agree with their rivalry, but would make for a great comic relief. They muck things up, and Flurry Heart is always cleaning up their mess. Lastly, we already know there's a love between Starlight Glimmer and Sunburst, why not add their child as the youngest of the group (of however many main characters), but being the wisest of them all, despite the youngest.
Anyways, just a couple thoughts while I finish my lunch. Probably a better fan fic..