Let's make some basic facts here. I think there is general consensus about these:
1. Powergamers will always have better skilled characters than those players who spend proportionally more time roleplaying.
2. The current system favours those with regularly a lot of time and stamina to powergame (eg, you can't decide to train "today" and spend rest of the week rp'ing, as you hit the cap on set intervals) over those who play more sporadically or only on certain days of the week or who simply like roleplaying better.
3. Currently, the only way you can gain skill is through investing RL time (t) in improving them.
4. As a by-product of the time-investment, you gain money (m). This comes through killing monsters/selling the underwear you knit, whatever.
Let us move a bit further and start making assumptions based on this:
A.) If the skill-gain is based solely on (t), then the players who are more capable/willing to spend excessive amounts of (t) to further the character skills will have a disproportionate advantage with skill-gaining compared to everyone else.
B.) If you can supplement the skillgain with (m) which the roleplayers also often have, this goes some distance to help them to gain skill in addition to the meager skillgain they already experience. There are characters who don't have (m), but it's not really argument against the system per se.
C.) If the status quo remains and (t) is the only way to gain skill without any parallel system, doesn't this mean that those who are least interested in actually training look forward to a future where they continue to be shafted the most skill-wise with zero shortcuts?
How to achieve a working system?
If we think that basic assumption 1.) is correct, then do we really have to worry about the powergamers at all? I mean, Matt (:P) will have a character with higher skills than mine anyway, simply because he cares and knows more about such things than me. He will have a skilled character regardless of the system. If we implement something which something helps him to achieve uber-level two hours faster than usually and gives the RP'ers an alternative way to increase skills every now and then (as opposed to not increasing the skills) then ..why not?
It's all matter of approach with the implementation. Some possibilities:
I.) Cap -> You can only get skills to a certain point through money (I'm not really sure if this is a good idea, though)
II.) Cap2 -> You can only buy points from certain number of skills (anti-alleskönner)
III.) Cooldown -> You have to wait an amount of time before you can buy skillpoints again, favouring a longer-term approach if the amount of time is also long.
I don't want a system where you just hit 50s to the table and gain 40 points in slashing, but something which helps RP'ers to develop their characters especially when they skill seldom. Powergamers really should have no part in equation when determining the viability of such system, as the guys will rock the world anyway and there's nothing we can do about that. We can, however design a system which acts on such long time-scale that it offers as little aid as possible for your average powergamer.
This, while taking money out of the game.
. A character that spends time with money and skill creating actions (e.g. crafting & selling to NPCs) can gain more skill by time - it don't think this is bad per se. Nevertheless, money is just one idea. How about other, sophisticated ideas? We already have one static quest that gives you a skill bonus and Keikan showed that it is extremly simple to script NPCs that raise skills, either for money or for other stuff. One example:
