Yes, new gambling sites can add altcoins withdrawal system. By following this, it may help them for marketing. It will be considered as a marketing tool for them which will help a lot to grow faster and also will he helpful for gamblers too. But we are doing withdraw with forcibly high withdrawal fee.
Not only that, they should have an internal swap or exchange. It's also a solution for most gamblers that find it hard to transfer and convert because they're too conservative about the fees.
They exchange internally with the altcoins of their choice and move it to their own wallets with cheap fee.
Actually there are already some internal exchangers that had been integrated in some known gambling sites but whats the issue? Fees are also high or they do charge up more
compared if you do just simply make out some conversion on exchangers but if you dont like to experience the hassle then you should deal with it.
This isnt already a new feature because some of them had already the internal exchangers which you can anytime use depending on your needs.