I assume we would handle this just like we did for v3, v4.0, v4.1, etc. that have reached end of life. We generally give people a LOT of warning and then finally pick a date way in the future that they have to upgrade. We're talking years though. I am afraid I do not have a clear answer to give you on such specifics that are many years away 🙂
As end of life approaches, you will get a lot more information on how to handle the upgrade. And, of course, by 2025 or 2026, v5 itself will be more mature. We might even be on v6 by then, who knows!