Earlier I advocated activities being gold-neutral. Rep grinds would give enough gold to pay for rep items. Kills and quests while leveling would give enough gold to pay for repairs, training, and mounts (excluding epic flying). Profession training would be paid for by vendoring crafted items, or selling it and the gold coming from the buyer vendoring something else; the net effect is that the crafting doesn't create or destroy gold.
Somehow I missed the other, possibly more important, part of the economy: materials.
Should professions require farming to level? I'm not suggesting that they shouldn't require materials, but how should we get those materials? Farming in this case is a non-leveling activity. This doesn't mean it can't be something that gives XP; for skinners that's nearly inevitable. But it's something done with the intent of gathering materials first and leveling second. Leveling might involve stumbling across herbs. Farming might involve stumbling across mobs.
Are professions part of leveling or are they an activity of their own? If they are not part of leveling, then we should have to farm; how much is likely to depend on the mood of the devs the day they place herb spawns and skinning tables. But, if they are part of leveling, then we should, on average, get enough materials to level a crafting profession by a 'normal' leveling pattern; some mix of instances and quests and possibly a mob grind here and there.
Note that everything is on average across the playerbase in a small range of levels. So maybe one player picks up more gold and the other picks up more skins. The idea is that there is vertical independence but possibly horizontal dependence.
Obviously if professions are not leveled while characters are leveling, then the professions will require farming. Again, this is on average; so maybe you don't farm mats but you farm gold and buy from someone who farmed mats, or someone who ran dual gathering professions; meaning that on average you still have a profession leveled while leveling (just not by the same person) and a profession not leveled while leveling (the gatherer), so someone must still farm.