Am I missing something? I haven't seen an unencrypted rom posted anywhere yet.
The big hurdle here will be flash support. Unless Tactrix upgrades ECUFlash (closed source) to include the proper handshake and microkernel for the BRZ, or makes their software open source, you'll need to solder the ECU to flash. Given that this ecu is on a new hardware platform, SHboot flashing may not exactly be straightforward.