To clarify, we are talking about "in order to be supported and have security updates" generally. For example if someone asks me how to resolve on issue on 3.4.7, my answer is "You need to upgrade to a supported release". So while yes, they 'need' to upgrade, I of course cannot force them to do so. There are still people who (strangely) run version 3 and have even seen a few custom jobs where people have upgraded from 2 recently.
However, people asking specifics about future events that have not even been spoken about yet, let alone planned. We can only really answer you based on what we have done previously.