We've talked about this in a few threads discussing how buying/selling would work. I think there are two levels to it.
The first is purchasing through consignment. So for example I need bat wings to make crunchies. I post a "buy order" with the local market broker for 100 bat wings at 3 silver each. I pay him a 10% fee of the total for his trouble. Then people can come and sell him bat wings for 3 silver each, and I can swing back buy and pick them up (or have them delivered to me).
The second would be an actual player contract system. So you would post a contract and say "hey, I'm looking for a Coldark Steel Longsword of Dragonslaying", along with the price you're willing to pay. A crafter could elect to fill that order for you.
In general, I think most of us are supportive of these sorts of things being options although a lot depends on how crafted items (or even loot drops) work. Simple buy orders probably wouldn't take much UI and database work to implement. Full-on contracts might be tougher from a technical perspective.
For me personally, I"m all for this, with the caveat that it can't break local markets. Meaning that if you put up a contract for a sword, that contract should only be visible in the town where you put it up - not globally.