As far as I understand it that would close the circle of melting cards into DEC and than purchasing new cards from the market.
This could probably lead to a highly lucrative trading environment because of the different arbitrage possibilities between DEC/Steem and Card values in Steem and in DEC.
I also see it from this perspective that I'm not anymore stucked with cards that are not really used by the community e.g. Dragon Whelp. I could than melt him down and get DEC for it and than go to the market and purchase the cards I want.