[K]

As this is a grand experiment, I'm tempted to "let the chips fall where they may" and not disallow anything.

I mean, if a dude casts the Arcane Nexus, they are asking for every remaining nation to send every assassination spell they can cast at that dude's provinces in order to kill the guy that cast the global (thus dropping it). You may have the gems for that turn, but what are you going to do with them when you have no commanders in your entire empire?

Natural selection and a glut of savvy players will curb even the most potentially abusive thing you can think of, and at the end of the day the ability to make a clam every turn is every bit one of Oceania's special powers as Abysia's ability to make a blood hunter every turn.

That being the case, I'd like to argue for no mods other than the ones to make the game possible. Let's not nerf nations because of what might happen before we even figure out what this play environment does to the game. Speculations are nice and everything, but lets actually get some testing in before we radically alter how the game plays.