Author here -- MIT does not currently have IPv6. Although MIT did receive a /24 IPv6 allocation, https://whois.arin.net/rest/net/NET6-2603-4000-1, it's not routable everywhere on campus yet.
Unfortunately, IPv6 deployment is still below 20% (as measured by Google, https://www.google.com/intl/en/ipv6/statistics.html) so a publically-accessible IPv6 address is not yet sufficient.