There are couple problems with it, the most important from my perspective is the fact that it goes against how I want HBD interest payments to be fixed. Current way is unnecessarily bloated and requires users to trigger payments by stirring their savings balance once a month (otherwise the interest won't compound) - from your perspective the key is that you can transfer to someone else's savings triggering interest payment on their account.
I think it should work exactly as vesting. Maybe we could even reuse mechanism of vesting routes that automatically tell where the output of "power down" should go (that would most likely not be necessary). However such change has a serious drawback from the perspective of what you want to achieve. While interest would be accumulating automatically without any user interaction, you'd have to use active key to pay out (even with defined routes), which means when you pass away without giving your family proper keys, they would not have access to the funds.

In conclusion, arrange your last will properly 😉