I would love something like this for personal use, so I can share my bank account with my family and control their spending and behavior.

I mean, assuming you can give out cards linked to said account, to discern who is using the account. That'd be incredibly useful. I used Google Wallet for this previously, and now use Simple, but it'd be nice to not have to approve requests and instead implement some logic to do so.

If anyone working for Simple sees this: get on this! I'd move from my main bank account to entirely Simple just for this functionality.