How is that even supposed to work? Wouldn't you have to prove somehow that you were a VIP at the other casino? And how's the customer support supposed to be sure you didn't just buy the email address and are trying to scam them?
Of course you need to prove the ownership of your VIP account in other casinos, it can be done in several ways depending on what is/are asked by the new casino to you when trying to pass the transfer process.
From my experience in 2 different casino, I only need to provide a screenshot of my account profile and I need to post a message on chat on the casino.
There can be other ways ofc, depending on the VIP program of the casino because every casino may have different way when it comes how to prove that we are the real owner of the account.
I don't know that you have that kind of ability with casinos to transfer somewhat your level/title with a specific casino to a new one. What casinos participate in that? I don't think that's good for business, though, if you are a casino owner. Please elaborate on this OP.
Metawin did it (even there were 2 seasons), blackjack.fun did it too, and some other casinos that I can mention one by one but some new casinos that popped up this year provided this program.
If it is being done properly and wisely, it is a great way to attract player especially high rollers because players can get a shorten way to get the benefits in the new casino without doing many things especially wagering.