Bitcoin transaction fees is starting to get more and more expensive for gamblers to deposit into their account on gambling sites, so I believe the market for altcoins will grow bigger in future on the gambling community, and we can surely expect to see more players wagering with altcoins.
In altcoins market we have a lot of choices and I hope more casinos will accept altcoins so it will give us a chance to gamble all the time.
Bitcoin is good but not this days due to the transaction fee and you cannot just bet small amount as the fee alone will already kill your bankroll, still majority are accepting only bitcoin but sooner they will realize that it will attract more customers when they start accepting altcoins.
I personally don't understand why all Bitcoin / cryptocurrency casinos don't accept the top 10 cryptos and just convert them into their own crypto and then you could exchange or use the equivalent value of the one you deposited (such as BTC, LTC, Monero, etc.) and cash out in one of those.
The days are over where BTC is the only player in the game. Now there are cryptos coming out left and right and nothing is going to stop that. BTC just needs to improve and hopefully soon because fees are through the roof (obviously).