As you have a d4s it would give you the best off both i suppose. Most d800e users would probably go the other way. I know I've thought about switching up or adding a d3s/d4/d4s and will do when/ if i ever get the funds that allow it. The DR and detail is great with the d800(E) and do wonder if I would miss that if switching to a d3s.
I wouldn't switch from a D800 to a D3s and I don't know anyone else that would unless they need the speed. I can't think why anyone who doesn't shoot sports, wildlife or press would sell a D800, and DOWNgrade to a bigger, heavier, lower resolution camera, especially if portrait and landscape is the main interest. What would they gain?
If landscape and portrait are the main uses for the D800, then I'd say definitely this is worth doing. You'll have the D4s for speed, the D800E for quality, and the Leica for travel and for when you need to be inconspicuous. Sounds like the best all-round solution to me.
The D800E is basically a D800 without the AA filtering, and does result in higher quality, but it's not a deal breaker. I owned both D800 and D800E for some time, and it's not a massive difference. If you print big though, the D800E is worth it. The D800E is the ideal landscape 35mm camera.
having owned both d800's i saw no more moire in shots with the E over the standard, its over played.
Likewise. I've never seen any moiré from the D800E since I bought it.
The D800E is a superb choice. Massive dynamic range, and quality is as good as it gets with a 35mm format (I've printed up to A0 and it holds well), and noise levels are pretty much up there with the D4s up to ISO3200, and there's not much in it at 6400 actually. Not an issue with landscapes and portraits though... usually.
[edit]
If big prints are where you're heading, you'll need good lenses.