I know this Edge/Del Rio feud hasn't started yet but for some reason it's just hard to care about this upcoming feud, it lacks any backstory other than 'champion vs contender' label, it just seems blah considering it's a WM world title program. IMO, this Edge/Del Rio feud needs third participant to turn its heat up, and that person should be either Christian, or my personal choice, Kofi Kingston.
The reason why Christian should be involved is obvious and OP has explained it well. And my alternative feud is that Kofi should also get involved in the Edge/Del Rio world title program. Kofi has started his feud with Del Rio, did you watch the Del Rio/Kofi/Swoggle segment on Smackdown? I gotta say that segment was very entertaining and showed that Del Rio and Kofi could have a great feud in the future, i love the aggression that both men showed and this kind of aggression is needed to make any feud exciting to watch. Kofi can make the Edge/Del Rio feud tons more interesting, WWE is all about the youths at this stage, Kofi is the current reigning IC champion and he doesn't have any contender for his title, i think he should get involved further in the upcoming Edge/Del Rio feud instead of just simply serving as a fodder to Del Rio at EC. WWE should build him up as a threat to Del Rio, if WWE has any balls, let Kofi go over Del Rio at EC and i'm sure this will benefit both men, Kofi wins against Del Rio in a convincing fashion and then Del Rio will try to injure him afterwards, this will keep Kofi's momentum yet at the same time giving Del Rio massive heel heat boost, i know this sounds very risky but it's worth a try to keep both men relevant instead of keeping one of them relevant while hurting the other. As for Edge, he already had a confrontation with Del Rio on Raw and Edge also had wronged Kofi in the past *coughsnowayout2009*, Kofi can also claim that he deserves a world title shot at WM since he beat a Royal Rumble winner and he has worked hard to get to where he is right now, and then Teddy Long will return and grants Kofi's wish, these backstories could potentially produce an intense, exciting world title program.
Kofi can deliver a strong match with anyone and is good at getting fan reaction during matches which will make any match more exciting to watch. Del Rio is pretty skilled, and Edge would need good opponents to have a great match these days (his matches with Miz have been terrible IMO), i'm sure these three can deliver in a triple threat match WM main event. Del Rio should come out as a winner, and then feuds with Kofi afterwards in a long intense feud which culminates in Kofi finally winning the world title at some point.