We will be having a state audit for CJIS. CJIS now requires 256 AES. All I can find online is the MX using 128 AES, and lots of AES information on Non-Meraki to Meraki.
Meraki was supposed to be moving to AES256, but I don't think I've seen anything officially announced. Might be worth it to call into support and ask them about this.