If Overstock starts trading their shares on Counterparty platform, there is a high chance that they will issue a OVRSTCK/BTC trading pair and that trading pair would enjoy most of the volume. As far as I know Counterparty allows asset-to-asset trading. CEO of Overstock being invested in Bitcoin and being the market maker for their own shares would be willing to support the price of Bitcoin, and would only need a small amount of XCP for transaction fees. Same would go for buyers of Overstock shares. It's not clear how this would help drive demand for XCP.