Having a level requirement for a game that is going to have actual classes for gatherers and crafters will make the market MORE inflated as opposed to less, imo. While it might limit the amount of control RMT are able to exert through crafting (but not through mats, depending on how one acquires those), it will make it so that a limited few people who actually want to level a crafting class will be able to make certain types of goods. Because there will be LESS people making them, their services and products will be lower in supply and higher in demand, driving the prices up. (In theory.)
It'll depend on how skilling ("leveling") up works as a Disciple of the Land. If it tedious just like the crafting system in FFXI was, I don't see the point in creating a "level" soft cap - the people who crafted religiously in FFXI will be the same people who level a crafter. Bear in mind, however, that people will be required to adventure to advance their craft, which is something players didn't have to do before. As someone who didn't craft much in FFXI (too tedious and expensive) and did lots in WoW (easy to level, not too expensive compared to XI, but crafting was essentially obsolete as a way to make money and I did it just for the ability to make certain armour "enchants" for all my toons), if I have to "level" my toon to craft, I won't do it. I want to focus on a class that will be effective in the storyline of the game.