I've been considering such a thing, but haven't tried it out yet. One of the players in my Forgotten Realms campaign is planning on specializing in item creation (although he's at 1st level and is an aasimar to boot, so it will be a while), so it will definitely have an impact.
The way I was thinking of doing it was to still require the feats, but knowing the feats doesn't necessarily give you the formulas; those must be acquired seperately, and only after you have the base feat. I'm not yet sure whether I want to apply this to the straightforward spell-storing items (potions, scrolls, staves, and wands), but I'll definitely apply it to everything else (this should help balance the grossly overpowered Craft Wondrous Item at least slightly). A player wanting to make an item will have three or four choices:
(1) Research the formula himself. This is obviously the only way to go if the character wants to make something that has never been made before.
(2) Acquire it in trade with another spellcaster.
(3) Find it in the spellbook or other book belonging to a defeated spellcaster.
(4) For wizards only, choose to gain an item formula in place of a spell learned at level-up.
I don't intend to force someone to spend years in research unless they are trying to create an artifact or something, though. I'm doing this for reasons of verisimilitude rather than an attempt to "power-down" something; it just doesn't seem reasonable that acquiring a spell should be a big deal, but any spellcaster automatically knows how to make any item that they want. But if it's down-powering you want, here are some ideas:
Require a Spellcraft check to learn an item formula acquired from another mage, in the same way that a Spellcraft check is needed to learn a found spell. If the check fails, the character has to wait until they gain a level before trying again.
Make acquiring new formulas from other casters even more difficult by having seperate formulas for arcane and divine casters, or even different classes within the same category--perhaps even different formulas for clerics of each god.
Since the components needed to create an item are now no longer common knowledge to spellcasters, it's difficult to find what you need for sale. The character must gather at least a few components himself for every type of item that he wishes to create. ("If I'd known that you needed mosfungus mushrooms gathered in the dark of the moon to make your potion, sir, I'd have surely gathered a few last time I passed through the Beoulve ancestral lands. But alas, I have none to sell you...")
Have the item creation process start when the base item is being made (as per 2E rules)--using special alloys or rare woods specified by the formula, for example, rather than simply allowing any old masterwork weapon to be used. This will probably require the PCs to learn Craft skills before they can make any item.
