First of all, the project needs to be a working product. That product can provide a wallet, casino, privacy, stock market service. If the product actually has a functioning mechanism, it means that the product can be invested. Just creating a cool whitepaper and creating a visually good website doesn't mean that altcoin will be successful.
If the coin is popular enough, the current casinos will add them to their supported coin list if there is enough demand for playing with the coin.
Just having a functioning mechanism won't make the coin a successful one. Look at those clone shit coins.