You can still play a gold dwarf. Purely cultural subraces like mountain and gold dwarfs can be done in backgrounds.
If there's an actual biological difference like with the elves they still get rules splitting them.
There are both magical and cultural differences. Magically, gold dwarves are usually born as twins and their features are less rugged. Culturally they have experienced less loss, endured fewer atrocities at the hands of monsters than other dwarven communities and thus more inclined to resolve conflicts with diplomacy instead of battle.
(slightly off topic - I prefer to think in terms of magical differences instead of biological ones. I don't believe that things like DNA, genes and the like exist in Faerun)
I get that 6e is going for a pizza shop model for species but if I'm going to design my own species I'll do that in my homebrew world. If I'm going to play a video game in Faerun I want to play one the races of Faerun.
