I'm not sure about the future value of 529's (though I have some for my grand-kids) but they have significant present day value in Virginia. If you run payments for qualified expenses through a 529 they are deductible from Va state income tax. (Up to $4000/year per account if you are under 70 with carryover to future years, unlimited if over 70 yo.) That can amount to a 5.75% savings.
It appears to me that most financial aid these days consists of loans. I like to see college graduates have as few loans as possible. So, I don't worry too much about the possible effect on financial aid.
The contributions to a 529 can always be withdrawn without penalty or taxes. I'm guessing that the 10% penalty on earnings (not used for qualified expenses) will go away if college is made free but taxes on earnings will not. I also don't really expect college to be entirely free, eg room and board, books, etc.