I do not really agree here actually. In my experience, crypto users are all Bitcoin people. Even when it comes to altcoin users, if they are real users, they have Bitcoin and spend it. The only people who have crypto and do not spend are altholders. I think BTC is enough in most cases to see if your casino has any players. Work on that first before expanding.
But if you have an exchange system,,, that would be useful.
What you are saying makes sense, but more payment types actually helps attract more and more gamblers which is why I partially agree with you here. There are times when the BTC network is congested and the fees are high which is when these altcoins prove to be helpful.
1 or 2 major cryptocurrencies like ETH, Ripple, Litecoin etc could help boost their subscriber base by providing more alternatives.
Will take a look on this about other cryptocurrencies that we can use for our site.