In the movie culture the answer to such questions is, of course: no real barriers, none.
There is no real barrier to entry, other than competence.
The tennis tradition was separation through the very real barriers of money and class.
There was no very real barrier between fantasy and reality in his mind.
But the real barrier was the way he moved.
The real barrier has been the time spent apart, he says.
This last may well be a real barrier to any products and will require some innovative thinking.
From what I can see of it, it's not specific to any particular race or kind, just a real barrier to everything.
That could be a real barrier to moving forward on it.
They are an important first step in eliminating the real barrier to retirement security.