It's between the artist and whomever is commissioning them. It's not DAs job to interfere unless something illegal or against the websites rules is involved. Also, it would probably discourage prospective commissioners from buying because they may feel they can't afford it, thereby cutting off an artist wages entirely.
I think dA should definitely encourage people to charge a reasonable price for their work but minimum wage varies so perhaps there should be more information on how to charge for your work?
A lot of young amatuer artists would have no idea what to charge people and often to come here to get their work noticed which is why dA should really be providing information on what a reasonable price for commissions would be, and the differences between amateur and professional art commission prices. That sorta stuff (:
Once people understand what a reasonable charge is, then it should be up to them to decide on the price.
Do not undervalue your work. If you do that, the whole market will be affected. If clients see that one artist is charging very low prices for their service, they'll think that it is okay to charge others at the same low price.
Although the situation varies from nation to nation and forcing is bad how the artist are treated in my country it's really sad and it could be said it's really because artists didn't ask for much since they wanted to draw. Now firms look down on so many artists saying you like to draw, why should I pay so much for making you happy. Again this is only the case of my country it isn't always applicable everywhere. However if someone is to price their work low they should understand they could be lowering the overall market price of any work in dA in the long run. In nutshell rather than forcing i think people should just keep such possibilities in mind.
Maybe a system that allows us to compare prices and standards. It is difficult to create a set standard for livable wages, since this is a global community and we all have different costs. What ma be below living wage for em might be above average for someone else. Perhaps we may want to look at it in terms of market place. And what buyers in various markets expect to see in terms of prices. Let alone Artist skill level and experience. Also there is also demand to consider. An artist in demand can charge more than one that isn't as well known.
I wish that I could have added something more useful to this conversation. Perhaps after I gain more experience with commissions systems, and get commissioned not to mention commissioning others to create art.
I have not read a lot of the comments but my opinion is that while in theory, it sounds amazing to have a minimum wage, it just cannot work here (or it can, but with a lot of work and research). As others have pointed out, there is such a wide array of skill levels and ages that it'd be difficult to justify certain set prices. Also, for example, 4 hours of work spent on an oil painting is very different form 4 hours spent on a digital piece (I am not at all saying that the oil or digital artist is more skilled than the other, but you have to take into consideration that the oil painter needs to buy materials and wait for paint to dry, etc.). Plus, there are many who get their name around by doing work for free or at very little cost (many masters have taught that this is something that is commonly overlooked by people who feel they are "too good", do not have the time, etc. Also, I think it would be a huge hassle for dA to create some sort of system while also monitoring what is going on. It's up to the artist to set a price and for the artist to be confident to stick to that price, move it up or down when need be, and even simply barter.
I haven't read all the comments here, so perhaps someone's already noted that, but I think that really cheap commissions may have a certain positive effect on how artists can "market" themselves as well. At least I have conscidered offering a couple of cheap commissions, to see if there would be an interest in what I do if nothing else.