@Kiryu
I think he actually stands a chance in RWBY.
Well now that he's in RWBY first thing he'll want to do is figure out his surroundings. If he's in Grimm territory then he dies. He can't control Grimm and he has no way to defend himelf. However if this is 8-A Lelouch, he has no problem with killing almost all of the Grimm. I'll assume this is 8-A Lelouch. (Let's assume he's in Vale too.)
Back to step 1, Lelouch is going to want to know where he's been dropped off. He has a chance of meeting literally anybody. If they're kind Lelouch won't waste his Geass and will try to pry information out of them. Probably will claim amnesia. If they threaten Lelouch, well Lelouch has his Geass or even his mech to help. Don't think he'd want to break out the big guns though, and he's more inclined to use his Geass.
For a while Lelouch will basically gather information. Maybe he will get someone to unlock aura if that's possible. He'd probably be interested in what it is but I don't know if he'd practice with it to get stronger. Lelouch has been shown to be nonathletic. Aura may or may not change his mind.
Lelouch pretty much will realize the only way to take over is to deal with the Grimm. They have the most territory in the world. He knows negative emotions draw them in so he needs to make sure no one is being negative. Thus he sets out to create a society where positivity is enforced and anyone rebelious will be executed. Kinda a dystopian future setting.
Now Lelouch just has to decide which faction should he join to begin his plans. The Faunus are pretty much the most relateable to what he did in Brittania. He'll have experience over the white fang/faunus. If he does join them, he may run into Roman, Cinder, Mercury, Emerald, Neo, and Adam. They'd be good additions to his army. Especially Cinder. Having a half-maiden will be quite the powerhouse. Especially if he can turn her into a full maiden. With that he can use her to take over Beacon. Take over the plans of the white fang and conquer Vale easily. The silver eyes issue may or may not come up due to Lelouch being in charge and he's much more inteligent at these kinds of missions. But if Cinder is wounded, Lelouch's mech should be able to take care of everything else. All he needs from Cinder is to take out Ozpin and the other 7-Bs and he's good to go. Though I'm not sure if Cinder can take down all the 7-Bs at once. Even with Adam at her side. That'll probably not be a good idea. As such, his research will have to be thorough to not run into trouble.
He may join Beacon to conduct research while also getting stronger without his mech. This could also help him in growing his army by recruiting people at Beacon. He could pretty much conqeur Vale in secret if he wanted, but that would take time. Unless Lelouch has a time limit he's comfortable playing the waiting game. That way he gets the councilmen in his pocket and he becomes the puppeteer of Vale.
Lelouch has shown he can handle a double life pretty easily, like Cinder. No one would Suspect him of being the badguy. Until the end that is where he reveals himself. He may just use his Zero persona though. He could fake his death too if it was impossible for him to still stick to RWBY's side. That way nobody would look for him if he did decide to go with the plan of attacking Beacon. He'd probably upgrade the stolen Atlesian Mechs too. With Gawain/Shinkiro he can follow their schematics. This process would take forever though considering Lelouch didn't build it and every part of it hasn't been invented on Remnant. Dust may also change how the Knightmares will be too. Lelouch's best bet to create this is to get to Atlas. They're pretty much the only guys who may be capable of building Knightmares. He'd have to get someone crazy to help him develop Knightmares though. Ironwood seems like he'd love them. With Ironwood Lelouch opens up a new door to Atlas. Maybe even Mistral at some point seeing as how Mistral and Atlas are buddies, but not much is really known about how Mistral operates so I can't really speculate what Lelouch would do there. Same goes for Vacuo. Menagerie is pretty much leaning towards the white fang so with the right push, and Lelouch controlling Adam, he can take control of Menagerie same with how he gained the support of the Elevens in Code Geass.
Close to world domination as it gets for now. We need to see more of RWBY's world to speculate his next plan. So far though he has Vale in the bag, Atlas in his palm, Mistral in Atlas's friends list, and Menagerie under his watchful, but discrete, eye.
I think I may be the first one to actually speculate on how Lelouch would take over a verse somehow.
