No I wouldn't like it. Bitcoin testnet should be reserved for development and should be free of charge and with no value in monetary terms.
When I visit the exchange where it's listed, it is said that you still can get it for free in its own dedicated faucet site. So, you can always head on it if you don't have money. Its value is only cheap, so even if we buy it it won't be a big deal. The only advantage of buying it is that we can get the coin immediately but obtaining it in a faucet can sometimes be a pain in the ass according to my experience before.
I see no need for it. I mean it's called "testnet" for a reason, it's solely for testing. Adding a monetary value to it would completely remove the idea that it's for testing and would pretty much remove the use case it was supposed to have.
If only the faucets in the casinos and then their free play/demo mode doesn't exist yet, this can still be considered for testing purposes. I don't mean to check the games if they are running well or if there are still some bugs on them but it's about testing a strategy, although I am referring to the classic testnet coins or the ones that don't have a real value and are listed in an exchange site.
This Bitcoin testnet that the OP is talking about is still a new thing, so you can say that it was still outside from what is considered to be a norm/normal but once it gained popularity or attention, that would be the time that casinos will now also include it as one of their options. That would also be the time that we will try it but for now, I think not yet because like you said the chance of losing on it is still high since the liquidity might still be low and then they can still decide to revert it from the old thing of not adding a real value on it because they can also realize that it is not really necessary and like you said it can only negate its true purpose from being a testnet coin.
