The problem I have with racial variants is that there's simply a lot of power creep in that department. In particular Eberron material has a lot of sick stuff for dragons, usually trading little or even nothing for powerful bonus. Unseelie fey on the other hand would be an auto-pick for monster classes with lower HD and Cha-based. Morale penalty on all saves equal to your Cha bonus whitout saves of any kind? Seriously? You're gonna tear trough everything if you have any kind of Cha-based save-or-die. So I personally wouldn't allow it, altough some people with love for really high powered games may.
As for dragonborn, I'll be honest and say I have no idea how it would work. Ok, tecnically it would strip you of all your cool racial abilities except stat bonus, but that's kinda crippling.