Its a nice idea, but you never can tell what smtp server the network will allow you to access if the SIM gets swapped, and there's no wifi connection. Also, you'd probably have to embed your mail account password in the script or something in order to be able to send mail from it.

Another thing worth thinking about is to always use passphrases with the ssh private keys you store on the device, so that those in physical possession of it can't gain access to other machines over ssh. That might make use of the reverse ssh connection somewhat difficult.

A question I have, is does the inbound SMS message destined for SMScond with a command in it get subverted away from the user interface so no notifications are presented?