To me, removing OHKO clause is probably the only one I'd be happy with. With such a fast paced metagame, you're really playing with fire if you're trying to use a 30% accurate to your advantage, over other more productive moves. Like barry has already said, it's all about risk vs. reward, and I personally think the risks of using OHKO moves are enough to outweigh the benefits. Given we are in a metagame where a single move/hit/miss could potentially decide the fate of a match, this isn't really making a huge difference (at least as far as I can see).
Evasion and Moody Clause, on the other hand, are the other side of the coin, IMO. If Double Team were not learned by pretty much every Pokemon that can learn a TM, maybe I'd be more inclined to think otherwise. It's too easy to spam Double Team and Moody, and the ways of countering it are quite inefficient. Moody is especially bullshit because it's not just Evasion, but it raises all your other stats faster than they drop them.
I'm not seeing removing Species Clause either. Sure, it's not inherently broken or uncompetitive, but my basic gripe is that it would just make shit a whole lot more boring. You can imagine someone just using 6 different Arceuses (which is probably a perfectly legit team). Species Clause is around to make our game more interesting because it forces you to use and learn different Pokemon. Ubers is not an official metagame, people only play it because it's fun and more interesting than the other tiers. Can you imagine our friendly Charizard noob being able to use 6 Charizards against you? That would turn me off playing Ubers pretty damn quick, IMO.
Not too sure about removing Sleep Clause, but not liking Darkrai being able to spam Dark Void at will.
Whatevs sig. QC member for OU and Ubers, VM me for a look at your analysis. Just make sure it's good.
Also, if you want me to rate your team (OU/DW OU/Ubers), give me a VM. If I don't rate it, it's either 1) it's so shit it's too much trouble, 2) I'm busy, or 3) the team is fantastic and I have nothing I can suggest to you. You should be able to recognise which one.