This behavior takes me back to how it used to function on Unreal Tournament servers (it still might). When you join the server, it would download the map, and then along with it any resources you would need to play on that server. Such as custom graphics, mods / mutators, etc.. It might function something like this:
1. Player ops to connect to server
2. Server requires 4 custom mods
3. Player downloads 4 mods immediately (from the server directly or from the official site?)
4. Player downloads map
5. Player's client toggles mods config to only activate those that are needed
6. Player joins server
7. ???
8. Profit!
![Uber Geek :ugeek:](./images/smilies/icon_e_ugeek.gif)
I believe some of the mods now are loaded when the game is launched, so this might cause some issues. As to where on Unreal Tournament, things are loaded when the player join a game/server. Perhaps a quick solution might be to just restart the game for the user and then attempt to connect immediately. This might be nice to have anyway because people could post a "link" that when clicked would trigger steam and load right into the game/server (but that's another topic).