Ore Trader (Currency Exchanger)

(Please read whole post as there are two different methods between first and second half of post)

[Throughout the post, 100 Diamond Ore is used for goal. The number next to iron is the amount required to get to 100 diamond ore but also the amount that will produce the amount next to silver. So the numbers are not additive, they are a sequence of exchanges/crafts that produce the next rarity of ore until the 100 diamond ore goal]

I've not really looked at past proposals for ore recipes and other ideas, but how about an NPC to run an ore market/exchange (like currency exchanges). Can use ore as a currency like Moolah to exchange for (buy) differing levels of ore. You can set a rate per upgrade ( /downgrade if feel the need) the same for all types or make different for all types. Following are some sample exchange amounts of each type to get to 100 diamond ore (the goal for many people), in 3 different tier of difficulties (I'll draw from Diablo III for the naming):

Normal (10x):
iron 1,000,000
silver 100,000
gold 10,000
platinum 1,000
diamond 100

Nightmare (15x):
iron 5,062,500
silver 337,500
gold 22,500
platinum 1,500
diamond 100

Hell (20x):
iron 16,000,000
silver 800,000
gold 40,000
platinum 2,000
diamond 100

Inferno (25x):
iron 39,062,500
silver 1,562,500
gold 62,500
platinum 2,500
diamond 100

As you can imagine, for Hell and Inferno mode's it's not really feasible to make all diamond from iron as it'd require 16 million and 39 million iron respectively. But it does provide a potential real use for lower level ore materials. If done by a vendor (particularly if can exchange in stacks) it does reduce crafting time from having to craft millions upon millions of times and makes it easily open to all players regardless of assistant skill choice or no assistant skill at all. Of course could also do it as a crafting recipe if you so choose.

The quantities are high, but realistically no one would rely exclusively on lower level ores, they would be getting diamond and platinum ores while mining (and a variety of other ores) or buying from AH/trading players. But it does provide a way to make use of the ore most players end up not using. Because of this, lower quantities of exchange than 10 seem unreasonable and too easy. As an example I'll list an easy mode of 5x ore per upgrade to the next level of ore and how much of each would be required for 100 diamond ore:

Easy (5x):
iron 62,500
silver 12,500
gold 2,500
platinum 500
diamond 100

Once again, it doesn't need to be the same amount per tier, maybe 2 iron = 1 silver and 5 silver = 1 gold and 10 gold = 1 platinum and 20 platinum = 1 diamond or something like that. Would probably be a more reasonable setup and preferred to the other options. Here is what that would look like as a path to 100 diamond ore:

Customized Tiers (2x, 5x, 10x, 20x):
iron 200,000
silver 100,000
gold 20,000
platinum 2,000
diamond 100

The choice would be up to you, these are all just recommendations with sample numbers to see how effective they would be. Please consider these options. This would reward any amount of mining, create new markets and encourage players to mine more. And now for the opinion portion, if you do decide to implement this and choose to use one of the above sample, my vote is for the customized tier sample, it makes the most sense and is reasonable/not unattainable while being balanced between rarity of loot.

Here as an extra throw in i'll toss in 1 advancement to customized tier so it is a little harder if you want (basically i'll just double everything), but it basically makes the higher rarities worse than the inferno tier, but easier on the lower:

Custom II(5x, 10x, 20x, 40x):
iron 4,000,000
silver 800,000
gold 80,000
platinum 4,000
diamond 100

All is up to Admin's of course, particularly the numbers/quantities used, but if you like the idea (or are opposed to it) of course feel free to comment below.

Edit: Add in a poll for those too lazy to post but want to give a generic response to let Sedy know what they think. If gets enough support/sedy likes the idea and doesn't want to choose numbers himself, can always do a second separate poll.