Jagex is going to make "gold merching" completely unprofitable. If you buy 1B at $450 with plans to resell for $550 and get that 1B wiped, that's a $450 loss and requires an additional 4.5B to be bought and resold successfully just to break even.
As others have mentioned, for now gold merchants will just have to make new accounts. Buy, sell, and dump the account. But at some point I expect newly created accounts to be insta-banned trading large amounts, because let's be real here... new accounts don't have any business trading around hundreds of millions let alone billions...