Maxperson
Morkus from Orkus
You don't need to shoehorn or "fit" Dragonborn into any official setting. Even the Forgotten Realms, which is by far the most detailed with lore, only spells out maybe 1% of the world's lore and population. I can drop in 100 new races and their lore without "fitting" or "shoehorning" them in. And I'd still have 98% of the world left to flesh out.The continuing argument about fitting or shoehorning Dragonborn into old settings is WHY 5.5e should get a new setting designed for 5.5e.
If you want a new setting, just ask for a new setting. Trying to pass it off as necessary for the 5.5e rules is easily seen through as, well, not necessary. You're better off just saying that there hasn't been a new setting in a while so you want one. There's no weak justification to see through with that argument.