When I saw the title of the thread, I thought it was a joke. Reading it, I see that it makes some sense but it won't completely solve the problem. Self-exclusion features have been around for a long time and implementing them globally I think would go a long way to reducing the problem, but there will always be those who, even if they self-exclude and can't play in legal casinos, will end up going to illegal games and losing everything.
The sad thing is that ideally, people should have enough self-control not to have to exclude themselves.
In my opinion, such a tool will not solve the problem of gambling addiction.
Gambling is caused by internal problems of a person. For example, a person has a boring and uninteresting life, so he spends all his time and money exclusively on gambling. If he self-limits himself in gambling, then the problem will not disappear anywhere.
I think you are right and that the person will externalise the problems in another way. In addiction to alcohol, drugs or sex, for example.
I do not know the country you come from, but mostly or nearly all countries, I even think even presently in all countries, no strict laws to know if a gambler in a gambling platform can be known on other gambling platforms, so the gamblers can resort to just gambling on other sites, or sites that are not well known as long as gambling that are even legit are still accessible. If the gambler can not gamble on other legit gambling platforms, but which I do not think is possible because they are many legit gambling platforms, he can then resort to just go the illegal way but which I do not think will happen as there are many other sites that are legit to go for.
Some people can have an interesting life and become addicted to gambling, so people can become addicted because they do not have job, thinking they can turn little to many through gambling, some people become addicted because they are thinking of gambling like they can be smarted and win more than lose, but they will later realize that and addiction become their problem. There are people that live a boring life and become addicted as there are people that live a lively life and also become addicted. There are people that live a boring life and never even thought of gambling.