I'd like to start off this topic by properly introducing myself, as I intend to lead a project with the goal of creation of a Halo mod for SC2.
My name is Nakamura(as you can see), a QA tester for Age of Mythology: Extended Edition, the project leader of the Age of Mythology: The titans Fan Patch, the Complex Enhanced mod for Homeworld 2 (and balancing associate of the Complex mod), and assisting developer of the Sins of the Prophets mod for Sins of a Solar empire. Some of these you may have heard of.
My focus as a mod developer is mainly in the design and balance area, and generally directing projects. I'm a quick learner when it comes to programming, however that is not my strength.
Recently I've played around with the thought of creating a Halo themed total conversion mod for Starcraft. Currently the team and myself don't have much experience with the SC2 editor, however none of us are new to modding.
Clearly Starcraft 2 is the best modern RTS out there, both when it comes to mechanics, accessibility to modding and the game itself (free arcade is HUGE for modders) along many, many positive features.
What I would like to do here is assembling a team that would be willing to carry through with this immense project – this is the thread’s main purpose.
As I said in the introduction, I'm already working with a team of a highly popular Halo mod for Sins of a Solar Empire. From my experience, there is no risk whatsoever.
The only time you're likely to have any monetary punishment taken against you in a court of law (In the United States) for something like this is if:
1. You're making money off of someone else's copyrighted work.
2. You're somehow causing damages to them that is preventing them from receiving money they would have otherwise received (which I think would be hard to prove for a mod, and pretty unlikely). It's probably easier to see this with pirating of movies. They could argue a person would have paid them money to see their movie had it not been for free online.
So if you're worried about something bad happening to it, the worst case scenario would be the mod getting taken down.
I honestly wouldn't worry about copywrite. If it gets super popular then Microsoft might do something about it, but honestly an SC2 Halo mod could never replace the actual game for a variety of obvious reasons. It's pretty safe to say that Microsoft wouldn't think it worth the time to come after you.
That being said, if the map does become popular, there's always the chance that Microsoft will ask you to take it down. Unlikely, but corporations have always done things that boggle my mind and make no sense to me, so you never know.
Such a mod will have issues due to the underlying concept of using Halo in the first place. You are not making a Halo mod for the good gameplay, you are making a Halo mod to feed off the popularity of Halo. The same game mechanics in some original universe would give you only a fraction of the number of plays you will get by branding it as a "Halo" mod. In fact the mod need not necessarily even be good as with a series like Halo the name alone would catch in thousands of players to play it at least once and people will even choose it repeatedly over technically superior maps purely on name alone.
This is blatant copyright infringement as you are using the popularity of intellectual property created by someone else to further your own mod. Due to the nature of StarCraft II Arcade and that Microsoft owns the involved intellectual property (which they are heavily using at the moment) you can be pretty sure you will run into legal problems.
If you want to develop a good mod then use your own intellectual property.