Excessive supply would act to reduce prices. Hopefully then we'd see a fall in gold sellers. Ofc, it all has to be balanced with the gold available in game...it might just end up relative.
But with the reduced demand for high end items that make your character more powerful, hopefully there will be less scope for sellers.
It remains to be seen whether the cosmetic items will just replace the powerful items from most MMOs that ppl chase and pay big bucks for. We'll just have to see.