Kee has the dns API available to it in Firefox since last year. It’s not supported in other browsers.
Since this would often be an asynchronous network operation, enabling it would delay all form fill operations, potentially for a long time.
There is no support for determining countries nor any built-in support for categorisation into private/loopback addresses so we’d have to bundle supporting code with the extension. In the case of blocking by countries, this would most likely require the user to configure an API key for whatever IP-country service they want to utilise, and a corresponding additional delay before any auto-fill operation can take place.
All things considered, I’m not sure this is something that we should focus effort on in the short term. Perhaps (at least for Firefox users) there are other extensions that might provide supporting information in the address bar or toolbar to help Kee users make a manual decision about whether to fill or submit the form?