I know. just hinting you not getting on the wrong road for ideas.
There has been it seems, two major discussion as to how to restrict capital ships, and these has obviously proven to be a complete failure - the thing is, capship restriction methods doesn't seems to exist. And I believe every idea were mentionned already.
There is just no viable solution in a server side modification that would force people to go on forum and learn to do rp to get a capship unfortunately.