@in reply to JohnV:
Let me try to add my .2cent on some of the aspects mentioned, ideally without writing a book - I hope you are aware of my appreciation for your thoughts, even though I may see things a little different.
You have asked the question wether WL is "ready to go on a new level", and expressed the feeling there were "moderator action" needed to achieve this. I disagree there.
WL is ready to go on what you call a new level as soon as the users are, and there is very little need to add/change anything:
So you want constructive feedback on some aspect of your track? Tell people in the track description: "I want feedback on my fingerstyle picking please, I'm not so much interested in sound feedback, since I am focusing on playing technique right now." and see what happens.
State the instrument & brand(s) of used devices in the description or the keywords/tags, and wikiloops will become a place where you can browse for sound examples matching instruments instantly.
If people would choose to upload lesson-kind tracks featuring explicit and easy to follow chord instructions, WL might serve as a lesson base just as well. Tag such tracks with "lesson", and they'll be very easy to find.
If users use the track descriptions and the "recording gear" section on their profiles to enlighten others about their workflow, or start a forum thread giving advice on a special case or to review a piece of equipment you feel is worth recommending, the "new level" could be reached without one change to the system.
Thing is, there seem to be quite a lot of people who are here just for the fun of it who do not care to state any of the above.
The process of "labeling" things correctly does not seem to be as much fun, and obviously there are other aspects than the "I would want to improve by getting feedback"-motive and the "I like to read how others do it"-interest some have expressed here.
WL caters to various interest groups and musical skill levels at the same time and leaves the users with the geatest possible individual freedom to use it in a way they enjoy- I do not necessaryly share or understand all of these ways myself, all I can tell is, it seems to work for quite a lot of people. It is a "running system" after all, so lets not forget about the good advice better not to touch that without good reason.
As I tried to explain above, you may use the offered system to communicate and educate on a "higher level", the choice rests with each one of us.
You have asked: [i]What about the uploaders who just want to make fun and would be displeased by some criticism?[/i]
I believe you are right wondering about that.
If you do not know anything about the motivation of the person uploading, about their musical education, their recording setup (closely tied to budget, as we all know), chances of criticising something the uploader was either well aware of or can't help are quite high -
if I upload for the sheer fun of it, and you give me feedback on which frequencies to filter, to spend money on equipment (which I can't) and to work on my german accent, then we don't really meet there. No matter how well you do in writing constructive criticism, if you lack information on my background, you can't really give matching advice.
I have a history of tracks containing lesson-type-approaches, sheer nonsense and tracks where I attempted to achieve something and was curious to know if people would have helpfull feedback - and I'd say I got the right kind of feedback on all of those, just by stating my expectations quite clearly.
So, if any, I'd repeat my advice: Ask for feedback/criticism on your points of interest in the track description, and don't go too far giving un-requested feedback, it might easily go wrong.