One of the most logical solutions would simply be to add a higher difficulty level to older Raids that reward you with upgraded gear to w/e the cap limit is at. If you wanted to get VoG armor for example that allowed you to reach Level 34, it would be justified by having to beat it on a Level 34 difficulty. However if hypothetically they did do this, I would like to see some physical changes made to make those Raids more challenging without taking the lazy approach by just increasing enemy level cap (aka what they did with VoG and not CE).