@jabean I feel like people are really over valuing diamonds in this discussion. They aren't at all hard to get if you put in the time to mine them; and "stockpiling" them isn't depleting the economy because they are realistically an infinitely expandable resource. If the amount of diamonds on this server was "fixed" and we all started out with a set amount and people hoarded them that would be the case but it isn't as anyone can go down to the lower Y levels and find them.
I prefer trading diamonds as the currency of choice because of their utilitarian nature and they provide an incentive for people to trade the rarer items like shulker boxes and beacons whenever I put out a purchase request for them; people who are looking to sell these items aren't going to want emeralds, even in bulk. As one of the "rich" players on this server I happily overpay or under-price items whenever I buy/sell because I don't view them as being super rare or hard to obtain. I think a lot of people like me who spend most of their time mining end up "stockpiling" diamonds because there simply isn't really anything out there that we can't obtain through mining so we don't have any incentive to add our diamonds into circulation.
It may be an unpopular opinion but I feel like the barter system/economy is working out really well for us compared to the last server as there aren't any OP villager trades and you're forced to negotiate with other players to get items you really want. On the last server I probably traded with other players a handful of times and did the bulk of my trading through the villagers in the TP and VIP lounges. I feel like the economy has gotten a lot better since the reset, but that is just my two cents.

Here's a screencap from today of one of my shulker boxes that I keep in my e-chest for proof as well as the stats page showing how many blocks I've mined since the last reset. Using mending on everything has pretty much eliminated any consumption of diamonds for me so everything I get is pretty much straight profit.

What you're describing here is EXACTLY the problem we're trying to solve! you might not have any use for diamonds, but players like me, who aren't rich, do. I don't have full diamond gear with mending and to me and a lot of other players diamonds are really necessary to progress in the game. emeralds however aren't necessary to progress and thus we can use them to trade. any diamonds that we obtain aren't used for trading or just looking pretty in a chest, but to make things wich we need to progress, therefor, using diamonds as currency is very inefficient and sometimes even impossible. then on the other hand, there are players like you, which just keep loads of diamonds in a chest without ever looking back to them. even if u don't want to buy stuff with it, you could still keep emeralds in there and sell the diamonds to players who actually need them.