The expansion is coming out very soon, and there is still going to be people working for the next Relic step for a while... I doubt they would make that progress useless for those people.

I have Zodiac, and I plan on grinding the next step as fast as I can, so I'm pretty sure I will have plenty of use for the weapon before the expansion, I know many who are still working on light farm or the dungeon drops from Zodiac part though... either on their main, or their alt(s). And the current Zodiac step came out like 3 months ago...

Fast forward another 3 months, and it's the end of May... Which should be just before the expansion, or even after it.

Like others have mentioned, they have confirmed they are working on something to make it worth it. That does pretty much confirm that you don't need to go through the current relic line to get the new weapons in 3.0 though...

I really hope it's some kind of shortcut for next relic weapons.