Probably it will be something like what we see at Bitsler and crypto-games, the available pairs are based on the accepted coins on the site only unless windice is preparing for a real exchange where they are planning to be like an exchange in usual but I doubt it. So the most possible scenario is the same like the sites I mentioned previously.
Casinos tend to accept very limited coins on their platforms, bitcoin, and a few of altcoins.
As you pointed out above, WinDice will most likely start their exchange in almost the same pattern of Bitsler and Crypto-Games.
If they decide to build their own real exchange, the project will turn out to become multi-platform projects, gambling casino, and crypto exchange.