Follower of the Way
The thing is, as I noted, they promised early on that everything in the PHB would be playable, and thus far they've done all except half-orc and dragonborn. Gnome was officially included in the most recent patch (patch 8), and a modder working to extend their existing expanded customization mod discovered (as I noted above) actual dragonborn heads. Further, there's several voice lines which depend on being a dragonborn--you can view them by setting a flag on your character save data marking you as a dragonborn rather than whatever race you're actually playing. It's not just a few, either; the githyanki party member, for instance, makes reference to the "blood of dragons" flowing in your veins after mentioning that there are red dragons serving Queen Vlaakith.Personally, I wouldn't mind if there are no dragonborn. After all, they include a couple of races that are not in the core rules. It's just a case of "this campaign has a curated list of playable races". Maybe dragonborn are not suitable hosts for mindflayer infestation?
Further, it's not like they have no experience working with reptilian humanoids. They made Divinity: Original Sin 2, after all. The Red Prince was an excellent, fully-fleshed-out character,* and custom PC lizards were also fully playable with a distinct story.
*I love playing the Red Prince, because not only is he tied to dragons, if you choose to play him as actually noble, not just a person of noble blood, he goes through a genuine transformation, coming to understand that the slavery practiced in his homeland is wrong and that great strength can come from egalitarian unity. His dialogue with the Lady Vengeance in particular is really cool if you have the Hero tag (easily acquired by just...being a good person on the prison island.) He's also a Snark Knight, with a delightfully acerbic Brit VA.