My guess is this:

The Zeta will last for a good chunk of Heavensward.
Once you hit 60, there will be a new quest for the new relic weapon.
Players who have obtained their Zeta's will get to skip the first few steps while those that did not get their Zeta will have to work through it to obtain their new relic weapon.
Players should have the choice to transfer over their stats from their Zeta onto their new weapons.
3.1 introduces the new upgraded relic line that will probably go for the entire 3.xx cycle.

Just some thoughts.