Cool. I've had a similar idea kicking around in my head for a few years. How do you think about the compromise/disclosure risk of the data you keep that associates the subscriber account with aliases?
Someone suggested the idea of creating hashed aliases, that are generated and hashed on the client side so that even I do not know what they are, then incoming emails are compared against this hash to determine where to forward emails.
The only thing is there would probably need to be an additional column on the hashed alias that is client side encrypted so that the user can still view the actual alias in their dashboard.
I've thought about tokens or credits that get consumed by checking/sending on the hash, but I imagine they'd be most-used for fire-and-forget stuff...