By the virtue of a larger community of package maintainers, the agenda can be more diverse and if that community is interested in maintaining older versions, that is a possibility. The scope of the current proposal makes it more feasible than before. I think we are in terms of infrastructure, community and process in a much better state than Fedora Legacy.
EPEL is in a different boat. It is a relatively young project, many of the latest software won't build on older releases etc and not really comparable to a extension of a existing release by six months just for security fixes.