If their plan is to use the relics from pre-expansion for the post expansion quest and upgrade, there would have to be significant nerfs to the current upgrade process as a whole. The reason for this is that when the expansion comes out significantly less of the population will be doing that content, which means that significantly less of the population will be able to help with the parts that cannot be soloed. Things like the fates and dungeons.

If this is their plan and they do not make major changes, then it seems their only other logical option would be to create a kind of catch up quest that would serve as the upgrade.