I appreciate the initiative, and would be on board of course.
Alien Invasion - YES, but needs to be thoroughly thought over before being started. We can't go too over the top or else our current tech standard nations wouldn't stand a chance. Albiet I do have orbital weapons, we'd still get our butts kicked.
Modern day world war - Already done before, and we've seen how that ended up being. It was a pretty successful roleplay save for a few instances of God Modding which can be fixed for the next time. However it may be okay to have a second war roleplay with different scenarios which would make our actions seem less similar to the previous one.
New Zombie RP - Not likely. We already have one technically still in motion, it just needs to get started back up.
And for other ideas, we can just take whats happening now, and put "what if" moments to them, or change outcomes so they happen differently. Butterfly Effects ftw.