I seem to think this is already the case - at least requiring insurance companies to offer the coverage to something like 26 as part of the package. If anything, making the parents list her is the new part. But you have been, by law, able to list your kids up to age 26, even if they are married or eligible for their own insurance.
What cannot be said is some Corporations who's employees kids are brainiac's and have a high propensity of said kids in College pursuing Degrees are costing said Corporations a fortune and they do not dare speak it and attract the ire of Lear Deader...