I don't really know what to say other than this is a really bad idea. They both share similarities, but saying you should rip out the entire story of Diablo 3 just because Dark Souls doesn't really have one or doesn't attempt to present it to you is stupid.
Of all things that Dark Souls does good and you argue for the one thing it doesn't even really attempt to do.
The similarities between the 2 titles are that they are both co-op and are both designed to be played repeatedly. The one thing I think Diablo 3 could learn from it is that Dark Souls is actually challenging on your very first playthrough, whereas Diablo 3 is a cakewalk and anyone who can left click a mouse can beat it on normal.
The last thing that comes to mind when thinking about Dark Souls is the story. Hell, even in it's minimalist state, it still makes mistakes like when it says all the dragons were destroyed... okay well then why am I still fighting dragons?
You are of course entitled to your opinion, but if you think that Diablo 3 had a good story, and Dark Souls a bad one, you are in the minority.
A quick glance at the story forum is enough to see that the majority of players are highly unsatisfied with D3's plot. Even if you personally disliked Dark Souls' minimalistic style, it's hard to defend D3's cliche and highly intrusive storyline.
I'm not saying that the plot of D3 should be "ripped out," or that Blizzard should copy major elements from Dark Souls; you're confusing content and presentation here. Diablo's content could certainly be more original, but my main point is that the story would be serviceable if it was presented in a much more nuanced manner - and I think DS provides a good example of how to do this.
Even if you don't like Dark Souls, the arguments that I made should stand on their own. If there is a specific point that you take issue to, I'd be glad to hear your feedback, but just calling my post stupid isn't very useful.