Scarfed Knock Off/Earthquake Krookodile will be very effective in RU. But of course, you need to have Hazards support, at least SR and 1 spikes. Have at least two walls in your team and make the opponent switch and take some switch-in damage. When all else is said and done, whip out Krookodile and sweep. Start with something that's low on HP and doesn't resist Knock Off. After you get to +2, almost nothing in the tier can stop it. Krookodile has the bulk to take the unboosted attacks of other Scarfers.
Delphox is a great SubCM user. You can have Sub/CM/Flamethrower/Grass Knot, but you miss out on Dragon and Fire types. Granted, there is only a few Dragons in RU and Fire types can't take a lot of switches because of SR.
Honchkrow stays the same, only more effective in a lower tier. Substitute/Sucker Punch/Brave Bird/Heat Wave can break through teams quite easily, if you play it right.
And I don't think Aggron is moving out of RU. Only Aggronite will be banned in RU. Aggron is too weak to too many commonly used types.
Edit: Ah, I forgot that. Then again, almost all Aggrons in UU are Mega Aggrons. Megas should be considered separately somehow. How is it anything but ridiculous to say that Mawile is banned in UU because Mega Mawile is in OU?