Tinashe will never have a hit as big as 2 On. And if she sold 18k then and have yet to put out another big hit, she's quite done. She'll be back to indie in no time.
I think in order for a black girl to blow up ala Bey and Rih, they have to be doing some kinda pop, crossover music. And they have to have a pretty big following and a hit making machine behind them. Out of all the new girls out now, Normani is the only 1 I can really see going solo in a year or two, releasing a multi format song like Work From Home and smash.