These are basic ideas that are on many servers. All this would do is 1. use more server resources, 2. split the players into long-term survival players and minigame players, and 3. require more updates and plugin designing that would take time from the devs who could be working on important updates to existing features.
I don't think just adding a basic gamemode will help because people can go to any other server to play these games.
However, if it was made unique enough to be different from most other servers, this could be a good idea. (I'm not saying it is guaranteed to work, look at mcmh duels. This server is already very dead.)