Implementing this would effectively destroy the economy. -1
Currently, you say that there is no market for nether brick--the lack of demand for nether brick implies that nobody really wants it. If nobody really wants it, why should the server establish a market for something when there's no demand?
Look at what happened last time the nether brick rush happened. Millions of meebles per day were introduced into the economy, causing runaway inflation. Prices of secondhand towns, God sets, etc. went through the roof, and it was just an all-around headache. Plus, with the addition of /smelt, Ultimates would dominate the market and drive everyone else out of business.