You need to look at this from the perspective of a new player. If someone joins the game, levels to 60, then discovers they need to go and grind old lvl 50 content that no one is interested in any more (i.e. good luck finding parties) in order to get their relic up to lvl 60 standard... well let's just say very few new players will be too happy about that. If they do continue the current relics into 3.0 then they will need to nerf it so that the previous stages take much much much less time and have zero requirements for party content simply because the queues for such content will be ridiculous.

In reality the more sensible option from a developer's point of view would be to grant some kind of perk for having completed the current zodiac but have an entirely new set of quests in 3.0 that starts everyone off on an even footing again.