no need to copy other servers
I don't think getting missions from NPCs is copying another server. It's in practically every single game out there with missions... It's the nature of the GTA SA story.
I have planned (like many other things) for a long time to implement NPCs that give you missions. Mainly story characters. The only existing part of this is The Truth standing at the weed farm in Whetstone. He says a line of dialogue but that's it.
I haven't got anything like that planned soon.