1. Cooling inlet underlip has become ridiculous now, going all the way upto chassis top. Massive, massive sidepod undercut. RB18 (rectangle) -> RB18 (thinner and wider rectange) -> RB19 (letterbox) RB19 (thinner letterbox) -> RB20 (invisible)
2. Engine cover shoulder looks like W14 Mercedes
3. Rear wing endplate bottom is extending backwards more. Could be a clue that the rear diffuser efficiency has been cranked up , which in turn could mean changes to the floor that is going to increase the downforce it can generate
4. I don't know whether it's an optical illusion, the front floor edge bargeboards look to be more 'forward extending towards the nose' than the RB19