IPV6 are not a issue especially abbreviated ones?
"short" IPv6 are still valid IPv6 addresses, and the checks are still done on the Stop Forum Spam side of things. We simply look for a "yes" or "no" from the request.
Example Request to SFSExample Response from SFS:
<response success="true">
<type>ip</type>
<appears>yes</appears>
<lastseen>2019-12-06 20:16:59</lastseen>
<frequency>12</frequency>
</response>