GameFreak is already working on the next games of the franchise, so far codenamed Lustrous Pearl and Iridescent Diamond.
It is not a remake, but a revisit to Sinnoh 30 years after the original Diamond and Pearl storyline.
You start off your jorney at Floaroma Town. Your rival, Maribel or Lucian, visits you from their hometown, Oreburgh City with their partner Aipom.
Aipom now has a different design and is Fighting type. You are both greeted by professor Maple, who is visiting Floaroma to learn more about pokemon living near honeytrees. She gifts you and your rival with starters after helping her find a Munchlax through a minigame.

This is all I saw in the rough, early-development footage.
The development team has a lot of new ideas for this "reboot".
> New forms for old pokemon brought by changes on Sinnoh's environment over those 30 years;
> No plans for national dex, but the Sinnoh dex will be revamped with new additons, forms and pokemon;
> Completely new story, and a lot of plans for the post-game, including the return of contests and the Battle Frontier.

Some of the new designs I was able to have a look at were Future Aipom and Shinx. Aipom likes to armwrestle and Shinx is a cute Ice-type with big teeth.
I was also able to see alternative evolution concepts for the starters (they are supposed to have a branched evolutions, keeping the old Infernape/Torterra/Empoleon trio but adding a new set of final evos). Chimchar has a branched Fire/Dark line, Piplup has a Water/Ice line and Turtwig has a Grass/Ghost line.

I will be posting more info as the games develop further.