I agree here- if the idea is that the Druid doesn't actually turn into a real bear or whatnot, and is still some kind of bear/dragonborn hybrid on the inside, then calling this out for all races, and giving some examples of what the limitations of Moon Druid wild shape are intended to be would be lovely. But of course, as always, it's up to the DM to figure out the intent.
Which would be fine if the rules could stand to be a little more clear about what the designers, at least, feel is/is not balanced. Instead of getting off the cuff comments like "oh what, dragonborn breath weapon in bear form? Perfectly fine!" to really muddy the waters.
Now I am mostly on the side of just saying everything works, because saying nothing works gets weird, when some races get things like skill proficiency as a feature. If the plasmoid is really goo with the appearance of a bear, or a changeling wants to look like a different colored bear, what's really the harm here?
That having been said, I'm sure there are some racial abilities that would problematic to be allowed for a Druid to use, like say the natural armor of a Tortle or something*.
*Not that I think this would be OP, the game already allows for Tortle Bladesingers, but more that a decent AC in beast form makes the choice better than other races, the very thing I'd rather avoid.
Basically, the fact that races are designed in such a way that some are just way better than others at certain concepts would be fine if WotC hasn't spent the past couple years undermining that concept. And any ruling that forces me to go over a racial package with a fine toothed comb to decide what you lose is, as I said, an unfun exercise.
Because any decision I'd make would be arbitrary, and again, would favor one character choice over another. Fine if we're playing 3.x style where system mastery is king*. But that's not really what 5e is supposed to be about.
*Though as an aside, 3.x did have a better description of what was gained/lost with wild shape, even though there were still massive imbalances.
I'm reminded of discussions about reincarnate, "hey if my Human becomes an Orc, I keep my mind and my bonus Feat!" vs. "Ugh, my Orc became a Human, so now I'm weaker and I have no racial abilities."
