Hi Airget,
Some great ideas here. :)
I really like the idea of having a Crafter affect Unique / Untradeable Dungeon / Raid Drops which would then allow a possible Melding to occur. It would certainly be a good way to involve Disciples of the Hand at two points in the process to upgrade and interact with Combat players.
It's also a good point about what happens if U/U Items break, but IMHO, I think allowing U/U Items to break if you fail a Double Meld would be good incentive for players to go through previous content again.
I agree that it may prevent newbies who've never gotten an item in the first place of being displaced (or fighting for a drop that others have already gotten before), but there is a saturation point where really old content is just undesirable (and most everyone who's gotten the drops are done with it) (e.g., Dzemael's drops).
And for sure, I agree, I'd love to see Disciples of the Land get involved somehow in the Max Level Content in some form. Your idea of allowing them to mine/chop/fish in special areas limited by the same system that limits Combat players is cool, but if the dropped Material only was from a Disciple of the Land getting it, what would the incentive be for a DoW / DoM to repeat content after they gain their drops?
It's definitely an interesting problem.
Perhaps, say, Ifrit did drop an "Orihalcum Ore" from the chest after beating it, but at a really low drop rate. But, tying into your idea, Disciples of the Land could also enter Ifrit's Bowl of Embers (separate instance) and have an attempt at a Gathering Challenge which would dramatically increase the drop rate of the Rare Items (like Orihalcum Ore).
At that point it would involve and incentivize both Combat Classes and Gatherers (and the Crafters would be able to help synth the super rare recipes). :)
