I don't have a source on this, but I think SE has said it in previous interviews.. While the 2.0 Relics will not carry over to 3.0. When the new Relics do come out, if you have a previous one it will help you "skip" steps when getting a new one (no idea if this pertains to DRK/AST/MCH) but it should to the Jobs that exist in 2.0. So that might be enough incentive to finish your one from 2.0 to Zeta.