I'll resist the urge to list off more of my favorite existing cartoons, as much as I'd like, say, Avatar sideshows.
Fantasy and sci fi is so good for animation in general. I'd love, say:
- A Baldurs Gate D&D party series in the style of DOTA: Dragon's Blood or Dungeon Meshi
- Mass Effect, maybe as stylized 3D, but with its signature bloom-heavy artstyle.
- Subnautica? Something about weird exploration on an uncharted world, like Scavengers Reign.
- Shadowrun. With dark cyberpunk style. Oh that would be sick.
- A Star Trekish-series but Sunless Skies-style steampunk. Or really just more Star Trek animation, that would be good too.
Many video games in general feel like they're begging to have spinoffs set in their constructed worlds (and an existing target audience to justify the animation budget). I can't think of as many examples I'd like based off, say, live action TV series and movies. And I feel like animation loses much its 'draw anything you can imagine' advantage in more 'mundane' IRL settings, as popular as that may be for anime.