yups, I think LN must be implemented in all casinos online as this is also the cheapest way to deposit specially when there are congestion and surely will come next year again.
Accepting Lightning Network for deposits and withdrawals will be cool for users but you must know that as a big business, they must consider more about security, risk and safety of their company treasury (wallet) and funds of their customers.
Lightning Network is less secure than Bitcoin network and risk of hack on Lightning Network is bigger. It is impossible to attack Bitcoin network and revert transactions after it has like 3 confirmations. It is main reason why adoption of Lightning Network in gambling industry has yet been big enough.