It would be interesting to see how it turns out. A strong reason why SmackDown suffers lower ratings is because, as mentioned above, far more of the target audience (18-35 year old males) are going out on a Friday night than they are on a Monday night, for obvious reason. Monday, your week just started, you have to go to work (school) the next day, you just want to sit down at 9 and watch TV, say hello to Raw. Friday, it's the weekend, you've got two days off, let's go out, get dinner, see a movie, have a drink, what have you.
Perhaps there may also be some talk about moving back to Thursday's, but in fact, SmackDown ratings went up in the move to Friday. Honestly, SmackDown is pulling very strong ratings in its timeslot and with it's demographic. Some may also state that MyNetwork TV is a problem, but really, SmackDown isn't pulling really any better or worse ratings than on CW.
It's doing solid, but the question is, why not Raw ratings? It has equivalent talent to Raw, in the Undertaker, Triple H, Jeff Hardy, Edge, etc., and the show doesn't really follow any greatly different format from Raw. The problem?
(A) Raw has a superior timeslot.
(B) Raw has a stronger history as being the "A-Show", even when it wasn't.
(C) And, to some small extent, Raw is live.
Raw is live is certainly not the strongest factor in the equation, but it's part of it. I think a live SmackDown would be interesting, and I'm sure it would help ratings, but I doubt it would pull up to equal Raw in ratings even so. Raw just has the timeslot and the history, and you can't change the history. There's also no real better timeslot for SD to move to other than the same as Raw, considering Thursday night wasn't doing as well as Friday night, and not to mention facing the (however small) competition from TNA on that night.
Overall, SD live could help, but it wouldn't do much. I don't see why not, but I don't really see a big why either.