Jackandor could be perfect for a one-shot. The audience wouldn't need knownledge of the lore.
An animated serie should be cheaper and faster to be produced.
The setting isn't so important but a good story.
A cartoon adapting the videogame Mythforce? I loved that 80's spirit in the trailer.
* The sequel of the 80's cartoon is other option. This time it would be a different group each season, and half group would be no-humans(gnomes, halflings, harengons, tabaxi, dragonborn, shifters).
Why not a G.I.Joe+Transformers: Isekai? Cobra used decepticon technology to create a stargate toward the origin planet of the Cobra-la aliens, and the plan almost didn't work. A new world is discovered, but this is secretly ruled by Cobra-la. Yes, it is a crazy idea, but so crazy even it may work.
Or an anime where characters from Kamigawa are sent within a virtual computer simulation.
* Nentir Vale was created to be a sandbox. This could allow more creative freedom to the producers and screenwritters, but there is also a risk when a lot of things start to be added, then there is a continuity to be kept.
* Why not Greyhawk with the iconic class characters of 3.5 Ed?