Okay, here's a first pass at some answers. Thanks for all the discussion so far.
Q: Why are you adding this system? What’s with the RNG?
A: The Netherlight Crucible (aside from being an important part of the 7.3 storyline) is intended to help with an issue with Relic availability that players have been reporting for some time now. As Ion explained during our last Q&A, there are technical issues with the way Relics were built that limit which bonus traits can be available from raids. This has caused a number of raiders to feel as though their best bet is to run Mythic Keystone dungeons constantly in the hopes of having a Relic with their ideal bonus trait drop (and Titanforge for a high item level).
Those who were following development of Patch 7.2 may recall an earlier take on an improvement for this issue, where we experimented with adding a single, randomized second bonus trait to Relics. Ultimately, we decided that was the wrong approach, and wanted a system that put a little more control in players’ hands. So, while the Netherlight Crucible does still have an element of randomness, it presents you with several options to choose from.
To be clear: we believe that having some element of randomness is important. Our goal was not to simply allow players to choose the precise bonus traits they wanted (you already do that, more or less, when spending Artifact Power). We still want there to be those exciting moments where a Relic gives you a great outcome. The Netherlight Crucible is intended to make Relics more valuable on average, not to make all Relics be equal value.
Q: Will I be able to trade Relics with other players to see who gets the best options at the Crucible?
A: No. Previewing a Relic at the Netherlight Crucible will bind it to your character and remove the ability to trade it. This is because those trait options don’t actually exist on the Relic until you attune it to the Crucible, in a process similar to enchanting a piece of gear. It also prevents raid teams from feeling like they need to send everyone who might be interested in a Relic back to the Vindicaar before continuing.
Q: Will the Netherlight Crucible work on Relics acquired prior to 7.3 release?
A: Yes. However, keep in mind that it will take some time (likely several weeks) to unlock the later stages of the Netherlight Crucible, where the additional bonus traits come in. We don’t expect that stockpiling Relics prior to 7.3 will give any real advantage in practice.
Q: Doesn’t this just mean I’ll want my best two traits on each Relic now?
A: For the hardcore min/maxer, yes, there will still be a “best” outcome for your Relic configuration. However, there are now more Relics that can achieve that state (as Relics with your second-best trait can now roll your best trait at the Crucible), and you’ll encounter fewer “bad” Relics along the way.
Q: Why do I have to go back to the Netherlight Crucible to upgrade my Relic? Didn’t you want to get away from mechanics like that?
A: Players often compare this to the old Reforging system, and our dislike of having to visit a vendor after each and every upgrade. That hasn’t changed. The Netherlight Crucible only affects Relics – you won’t need to visit the Crucible every time you pick up a new pair of boots.