As explained previously:
Many items are going to crash, consequences:
Items become cheaper, less gold needs to be bought to acquire them.
Items become cheaper, gold conversion activities (selling to stores, alching, ...) become more popular, resulting in more gold in game (further devaluation of gold).
The grand exchange will affect both supply and demand, in an unfavorable way (for goldsellers at least).
Also, if you'll want to keep undercutting the market you'll have to go even lower, so it would make a change for you.