I guess this is the economically efficient solution. The main problem is that it needs to be administered by the government, for practical reasons as well as adverse selection. In Australia it also happens that the top 5 universities are of roughly equal quality, and the next 5 are not far below, so that a one-size-fits-all approach makes sense (there are no good private universities in Australia). I don't see how this system could work in the US where there is such a wide range of qualities in universities.