Regarding Greyhawk. The Dragon Magazine map of planet Oerth is official, in the sense that it appears in the 3e Living Greyhawk Gazetteer.
On the other hand, the Oerth map itself is presented by an unreliable narrator, and if a "medieval map" might include significant spatial distortions of size and rotation.
The farther from Flanaess, the more a future official map can redraw the map, if necessary. When the Oerth map came out, it got mixed reviews (love and hate). So today an actual world map for D&D 24 would do well to go thru a UA feedback check.
In any case, Dragons Island is right in the edge of the known world of Flanaess, and part of the area for a Dragonborn civilization can even be seen. The location of Dragons Island is secure, and it is a large landmass. There can be diverse Dragonborn cultures, including multispecies cultures.
This thread calls for a "new setting" to be more inclusive of the Dragonborn. But this doesnt necessarily require a new planet, a new world setting. It can be a new regional setting that earlier products had not elaborated yet. Namely, Dragons Island.
There is a Dragonborn population in Ket, evidencing the Dragonborn include mercantile cultures following the land traderoutes. Additionally they probably have significant naval cultures as well, following sea traderoutes, albeit these are more distant, needing to circumnavigate the Zindia subcontinent before reaching Flanaess.