I think I finally cracked it: either that, or I just finally cracked.
One of the classic problems with D&D in terms of crafting was that it is a skill points-based game where as long as you simply invest the points, you can use the skill. So, if you have the points to invest, you could, say, invest 4 points in Auto Repair and be able to build (albeit crudely) a car out of spray cheese containers. But for a MMO, you want people to have to spend time with crafting, as it allows them to have something to spend their time on (which means: a reason to keep paying the MMO company) and it helps to make the generally powerful items available from crafting seem somehow reasonable.
So, with D&D, you end up with a conundrum: do you preserve the sanctity of the points system (as in DDO) by creating a system of crafting that has nothing/little to do with D&D's skill points, do you throw out the points system in favor of a time-based system (A lot of NWN player-run worlds did this), or do you simply grin and bear it, ignoring the fallout of using just skill points (as in NWN2)? What I came up with this morning in my insomniomatic dreaming was a combination of skills and time, one that I've never seen anywhere before (this question hadn't really bothered me before about 3 minutes before I sat down to write this blog entry) but that I think could be epically good.
So, here's the idea:
1. Skillpoints are an after-the-fact purchase. Like with other games, you could have a skills trainer who is separate from the level-up mechanism. You go to this skills trainer when you're ready to purchase a new skill.
2. Raising a skill still requires skill points, and you receive them just like you always would in D&D. You just can't spend them yet (see #3).
3. Skills themselves have training requirements necessary for purchase. So, let's take the example of our Auto Repair skill: you start off untrained and unable to use the skill. You find the trainer for Auto Repair, spend a skill point, and she unlocks the ability for you to learn Auto Repair. Now you have 1 skill point, but right there with the trainer you can practice a few small things, using your skill on the target components or vehicle a few times (leveling anything from 1 to 2 is always the easiest, after all), and that will build up an experience meter for the skill itself. Once it reaches the XP needed for level 2 in that skill, you return to the trainer, spend 1 skill point, and voila! you are now level 2 in that skill.
4. If you don't have the skill point to spend, the skill simply remains capped until you do.
5. If your skill is already max for your level, additional uses of the skill do not build the skill up further. So, just throwing out some crazy numbers, let's say you're level 99 and the max skill value for level 99 is 370. You can't build past 370 to have it ready to spend a skill point on 371 when you hit 100 (of course, chances are you haven't managed to build the skill that far yet - it'll probably take a bit of grinding to build the skill once you hit 100, that's just the nature of MMOs).
This kind of returns to the roots of D&D, as the intention for skills was always that you should have to spend time with them in the game to actually get them. It was up to the Dungeon Master to make sure that you did only purchase things that reflected the skills you used in the game, thus training only what you've experienced. Additionally, it could be used for other things as well, skills that don't have a crafting component, for instance, to help make sure that people don't simply grab them up willy-nilly and become awesome without putting in the legwork.
disclaimer: This is my own creation without conscious influence from outside sources. I have posted it here with the intent that it now becomes property of the world at large - I want no part of it. It is much more important to me to see my vision implemented in an MMO than to ever consider requesting payment for said vision. So, if you're a developer and want to use this idea - please do! I'd also love it if you dropped me a line on mmorpg.com to tell me that you liked it.