Nice idea, and that isn't even mutually exclusive with an online version. Having this as a website definitely has advantages - you can easily set up a monthly payment, the receiver gets semi-reliable recurring income rather than sporadic one-off donations, you can pay by direct debit.

I think the real problem would be what is the meta-tag? There isn't really a standard for "send money to this URL". You could support Paypal I guess, but do they have an API for sending money? And then you're reliant on Paypal which is fairly notorious for just cutting off anything vaguely unusual (like this would be) and keeping the money.