There is also this line in the article:
Melissa Carter said it's her "understanding" that her son will have to do two years of military service if the bill gets passed as written. (Army officials explained that after two years of active service, a graduate can apply for an alternative service option.)
I think the era prior to immediate waivers was sort of the David Robinson era where he served 2 of his 5 year commitment and then deferred the rest to reserve duty (and frankly PR for the Navy).
Since Song has already done his first 2 years and that was immediately after graduation, he has probably surpassed the new requirements. For the Phillies it would probably best if he cut a deal to complete his 3rd year and stay through the Summer and then get activated in the Fall so he could spend a month or two getting in shape before going to the Arizona League which could be his "minor league career" before having to make the major league roster in 2024.