I see no problem with this.
Besides, the men's side has allowed specialization for ages (and has never had mobility scores at all), and competitions are still dominated by all-arounders. I suspect that with women, who only have four events (three of which are floor), specialization will be even less common than with men.
And it still hasn't happened within the levels as it's been allowed, just as a way to get to regionals or whatever. I really have only seen it with older girls in extenuating circumstances. I think most optional coaches are looking ahead developmentally, and they aren't going to sacrifice an event that could be improved long term just to get some short term gain (nor are many optional families and gymnasts going to accept that). It would have to be a decision in the long run best interest, and I think in almost all cases until the girl is much closer to NCAA gymnastics, it wouldn't make sense to discard an event. Plus, with the training format of most gyms, it would be inconvenient to have a bunch of young optionals just training all these random events, rather than all four together.