Adding missions to GunZ would be a huge project, don't think we would ever have the time to add such thing.
For the activity points we can also adjust the conditions. Say that for 3 hours you need 50 kills and/or 1 million XP, we could make it that for 2 hours you need 150 kills and/or 10 million XP and for 1 hour you need 200 kills and/or 20 million XP. Of course these are just examples.