When these were first introduced these were actually very fun, but honestly they have turned into a joke in the game now. The loot that makes them the reliquary is laughable even in the beginning of the expansion. These "special" super rare crates should be reserved for rare items, adorns, etc that would be beneficial through the majority of the expansion. Just a thought
It's a special loot chest with a special appearance and name. Reliquaries are rarer than Exquisite Chests and (by definition) contain an item flagged as Relic or Greater Relic. A common complaint this expansion has been that Relic items aren't as cool as they should be.
They only show up in VoV for the most part. I've seen them in Kunark Ascending, I think it was. They're better than Exquisite chests. The issue is that Exquisite chests themselves have become common. Anything of Fabled quality will result in a master chest dropping, only for players to yet again find another common mercenary gear or that silly mount that people are always trying to give away. Now if you get a Reliquary, that means you found a slightly better mercenary gear than what you get from the exquisite chest. The issue is the coding of the quality of gear vs how expected it will be used. Back in the day when you saw an exquisite chest, you knew a Master spell or a very unique item would be inside it, but VoV has an issue with how common everything but masters spells themselves have become.
I'd also add that the reliquaries I've seen solo, grouping, in raids, etc. have been dropping "ho hum" loot. Certainly nothing to write home to Mom about.
Like everything in the game, the gear is suffering from inflation. There was a time when legendary gear were desired gear upgrades, not just starter gear to be tossed as soon as possible. Now that fabled gear has become commonplace and obtainable from solo content, I wonder what the next step will be.
I get it... they really left themselves nowhere to go once every chest in every heroic instance started being Exquisite. It's another example of when everything is "special," nothing is. My wife refers to it as "chest bloat."