I haven’t heard of anything around SHA512 for the Meraki MX appliances, and I know a number of other vendors support it. I’d open a case with support just to check whether or not there is something they’re able to turn on for your network to support it. Other than that your best bet is to reach out to your local Meraki SE or AM to see if they can provide some information (it’s unusual to get forward looking information here).
If you do use the Meraki MX for your connection, just remember that third party site-to-site VPN routes aren’t shared across AutoVPN connections (just in case you have any). This means it’s often easier to use a different firewall (like a Cisco FTD or ASA) for such connections, then static routes to/from the MX - that may solve two problems, the SHA512 issue, and the sharing routes over AutoVPN.
