Personally I think they should offer it right out of AIT to Combat Arms to those who want it. If you get rolled you head to your first duty station
It would be the perfect time for it. It would be before the soldier has a combat mission and has the most to learn. No reason that the OSUT Commander couldn't have a certain number of slots assigned to give to soldiers on a merit basis. You could also give early promotions based on completion to further motivate our young 11 bravos. They already have the PreRanger course available for this scenario. I have not been to Ranger School so I admittedly do not understand how the dynamics of this would work in the actual course.