Preferable way to open up a game mode for easy modification?

[Strideynet]

Howdy,
Once I finish the gamemode I'm currently working on I'm considering reworking a major but old gamemode that has fallen to pieces and is a rubbish port ( Basewars!). I want to make sure that it is very open to modficiation but want to know how people would prefer that this is done if they were producing a mod for this. I want it to allow the most flexibility to modders, to make an experience even easier than modding for DarkRP

I'm faced by a small selection of options and I don't see real benefits over each one. I can offer a module system where a folder can be placed under the gamemode and be loaded in. Although, I believe this wouldn't make updates an easy procedure. Another option I see is making sure everything is opened up so that a normal addon can be created to interact with the game mode. Apart from assistance with this choice is there anything else, apart from sexy documentation, that would make modding easier for you guys?