Dwarf and poison.

[Dire Bare]

Compared to the anguish of having to somehow cram tiefling and dragonborn nations and history into long-established campaigns, or explain why ancient wizards had Wish and Time Stop but today's wizards are non-quadratic, this ranks pretty low on the aggravation scale in my opinion.

Anguish? Heh, heh. I found it pretty easy. I kept the same rational for tieflings in 4e that I did in my 3e campaign, they are either planar characters (aka Planescape) or they are a "cursed birth" resulting from mysterious diabolic influence. Dragonborn were part of a planar incursion, an invading force from another world that became trapped on my campaign world. I missed all that anguish.

Also, as wizards are rare in my world (not as PCs, but as NPCs), what spells they did and did not have access too or how they worked never really came up.

Dwarves completely immune to poison? Also easy. Plus, I like it! If WotC drops this feature from D&D Next, I just might add in back in for my home game!

And, ultimately, if I feel dragonborn, tieflings, and unpoisonable dwarves are just too much for my campaign, I'll skip all that anguish and just houserule them out.