Well, sadly for the research, not so much for the twins, I think it is less likely that in the future there will be a significant population of twins separated at birth to study. No ethical agency would do it. Of course, there are still unethical agencies--I know of twins my dd's age who were adopted to different families as infants, U.S. parents only found out after adoptions were completed, and one family relocated across the country so that twins would grow up together.