It would be good though. In other MMOs whenever player market exists alongside NPC traders it's for the purpose of getting items that require some work to obtain. Imagine being able to buy/sell fully engineered modules for twice (or more) the price of base modules, or being able to buy guardian modules without going through the grind of unlocking them. That would bring a new way to exchanging credits for grind, or grind for credits (just like in other MMOs).
Of course that would undermine FDev's monopoly on market prices (and the means to obtain credits), as well as the necessity to spend hours upon hours of gathering materials yourself (which constitutes a large portion of "content"), so doubt that's ever going to happen.