Or lock down consoles to only have one regions accounts on it.
Or lock down game sharing between regions. They lock down DLC. There is no way it would be that hard to lock down if They really wanted to.
All of this is opening up a lot of deeper issues the more I think about it. Locking a console to one region would mean needing to allow changing regions, since if you move then the console is basically not usable unless you abandon your account. And that doesn't just mean moving between countries. Different States have different tax rules for digital purchases (pro tip, if you're making a US account, set your address to Oregon, they have no tax on the PSN store), simply crossing state lines would lock anyone else out of your console. They would really need to chose if they want to upset a lot of legitimate users of the feature just to stop people from abusing it.
And DLC is locked to the regional version of the game, it's not a restriction on Sony's part, it's an ESRB/PEGI restriction.
If they really wanted to, they could, but there are a lot more legitimate users of gamesharing that you'd impact in the process.
I'm happy to just not tempt them