Should they be allowed? Having played through the era of 'a warforged, a vampire, and a werewolf walk into a bar in Elturel' era of Living Forgotten Realms, I really don't see that the 'kitchen sink' approach to player options really improved the game experience all that much. It gave people with 'shiny object syndrome' an excuse to show up for a couple more sessions, but they lost interest in those shinies pretty quickly as well. I'd much rather see a dedicated setting book with the different Realms-specific racial options specified.
Will they be allowed? We'll know in a few weeks when the revised Player's Guide comes out, but I'm not holding out much hope that the voices of restraint will win the day here.