Well you could say that stratifying our education system with anything other than mainstream public education will impact the overall level of achievement of the average Australian student (i.e., whilst selective schools excel the advanced students, perhaps a side-effect is the diminishing education of average students)... Potentially impacting on a host of other things like future productivity in a roundabout way.
Basically... how does the general public school class work?
You've got the super high-achievers, the middle band, and those that are really struggling.
Usually, the 'lower' two bands will ask the high-achievers "bro how do you get the answer", and high-achievers will end up taking on roles like unofficial teachers who aid the 'lower' bands. Additionally, having that top tier could motivate the middle band to work harder in their education because they see what's possible.
Now, if you took out all the high-achievers from this system, our public education is left with two categories - low-performning students and middle performing students. The former of which aren't able to receive peer-to-peer assistance, and the latter who grow up thinking they're quite smart (because they are, relative to the performing peers), and as such, never really put the extra work into their education.
So, yada yada, etc etc, removing smart kids from mainstream education could have drastic impacts on our national educational levels which are all ready in trouble, and therefore, it shouldn't be done.
Another point: perhaps narrowing their focus on science too soon will actually make these students worse at science. After all, the best scientists have a broad education (not necessarily formal) in the arts, philosophy, and so on. Perhaps the aim for our budding scientists in high-school should be breadth instead of depth, before allowing them to take advanced university streams in narrower areas.
Note: I don't believe a word I'm saying.