As others note, it's already possible to remotely wipe/lock a stolen phone, and if you report it stolen to the carrier, they'll list the IMEI in a database shar

As others note, it's already possible to remotely wipe/lock a stolen phone, and if you report it stolen to the carrier, they'll list the IMEI in a database shared to other carriers; many will refuse to activate/connect when their SIM is inserted into a phone with a known-stolen IMEI. Short of visibly, physically destroying the phone, though, there's nothing you can do to prevent this. A criminal doesn't care that the phone is a brick; they'll sell it to someone and be miles away with the money before the buyer realizes the phone is useless.