How would you feel if instead of making Half-Life: Security a proper mod, I just made it as a Sven Co-op map pack? Do many people on this site own Sven Co-op? If I did, it would be both SP and Co-op...and ti would mean I don't have to do any coding at all. The only downside to this is that if hardly anyone owns Sven Co-op, they won't be able to play it...since I'm not gonna put up a massive mod containing all of Sven's vital files. I'll then have to advertise it on the Sven forums...
It would still be a mod...sort of...there will still be new models included.