Let's just jump right into it, shall we?
I actually like this change quite a bit. Yes, I am capable of liking things. It's not all whining about haste over here.
What I like about it is that it emphasizes Overpower over autoattacks, which are fairly unimportant for an arms warrior anyway. You hit cap at 7.5%, which is absurdly easy in comparison to fury anyway (which is why no fury warrior bothers to try, leaving hit a fairly pointless DPS statistic... but we've talked about hit and expertise before) so you're going to land those slow hits and generate rage with them... and that's pretty much all they should do, in my opinion. With Mortal Strike and Colossus Smash both so important, giving Overpower more to do is fine by me.
I also absolutely agree with the idea of making Execute completely discount Overpower's rage cost. In fact, I agree with it so strongly that I'm sort of bemused here. Usually I don't wholeheartedly endorse a proposed change.