I think you misunderstand the current system. There is a 5% fee right now (unless set specifically lower by the the person/bot listing something). If the sale happens on the Splinterlands market, the set fee goes to Splinterlands. If the sale happens on a 3rd party market, Splinterlands is getting 0% and the fee goes to the market where the sale took place.

This proposal does not change that, it just proposes to set the fee to a fixed 6% from which 2% are burned.