I get your point, but I think what your describing isn't particularly meaningful. By definition, nearly 50% of any population is categorically an undesirable surplus.
To a certain extent, this principle is applied today. But I imagine it could be scaled up to something akin to highly selective university admissions process (e.g. interviews, standardized testing, resume critique, references). If a country starts with sufficient desirability, this could result in a positive feedback loop -- an increasingly competent and productive society.
That is simply not true. Most countries do not have the demand, willpower or money to sustain, say, a world-class research institution.