Quite simply, whatever the eighth race, a lot of people would find it unappealing. The same with the flavor and/or name of the dragonborn (again, what's wrong with the name?).
As long as we don't have the actual PHB in our hands, so we can make statements and comparisions based on actual rules and finalized (generic) fluff, all we have are the WotC tidbits and everybody's personal ideas and opinions.
And those ideas and opinions are naturally going to diverge a lot. Look at the gnome fans, and the people who never cared for gnomes; or the elf fans and elf haters; people who think D&D should be more Tolkien, or less Tolkien; more sword-and-sorcery, or less; the gamers who like wizards over fighters, and vice versa...
Seriously, no single race, no matter how creative, is going to please the whole D&D audience, or even a majority of it. The thing is, can people live with races and other stuff that doesn't exactly match what they'd wanted? Of course; we've been doing that for years and years, in all the previous editions. (And if we can't, we can houserule things. That's been done, too.)