They would basically become public schools. They would demand equal money from the government. You would need to take funds away from science and technology and fund "art appreciation". And that's just the beginning to this disastrous plan.
On the Issues: It's Time to Make College Tuition Free and Debt Free
Look retard, there is no way to make all colleges free as some charge hundreds of thousands of dollars per year and some just a fraction of that. Since they are private not public, the government can not regulate their cost, what you are proposing is pure communism, which would render the constitution null and void. So it is impossible, just like your breaking 100 on an IQ test.