I don’t think that’s an issue. Just don’t let them run raids in Chromie Time if raids are a concern. And since it’s capped at 50, the gear should stay capped at 50, right? And new zone gear is always a higher ilevel than old expansion quest and dungeon gear.
Or just do it the easy way: don’t let you earn gear. Just a small amount of gold. People want to go back to run this for fun, not to gear. So I feel it would be easy to just say “no gear loot for you if you’re going back to run this at 50+ and be scaled down.”