I would personally love to see both modes played alternatively on the same server. It's a refreshing break and it gives everybody a "guaranteed" knowledge of map cycle.
If joe pubber is playing NS classic and after a round gets sick of it, you can play a map of ns combat easily. Same goes visa-versa.
Having 2 servers would be a seperate option, but then you'd get the problem of splitting the playerbase of the server. If Player A says "Let's play combat. I'm going to the combat server" and half the people go, but half remain, you end up in getting some pretty unenjoyable games. I have to say combat is quite fun with large player groups, as is NS.
That being said, my vote is cast for mapcycling running both types of game alternatively. Once 3.0 is public, people are going to come to Lunixmonster for the name and for the playerbase. But they're also going to want to play Combat probably more than anything. I say if you give them even doses of each game before making a set decision, you're good to go.