I'm cautiously optimistic. Honestly, I've seen the original several times, and Klaatu is quite wooden as an emotional source- Keanu Reeves (with his reputation) is one of the first actors I'd consider for reprising the role, not last. Besides the fact that he's known for being fairly one-note in most of his performances, he's pushing 50 now isn't he? That's the perfect age for Klaatu, given what he was like in the original movie. Modern effects for the ship, robot, and weapons of the robot (not to mention communication and resurrection gear) could do wonders for it.
As for switching off electricity for half an hour- you think the 50s people went nutso, just think what we of today would lose with that! No TVs. No stoplights. No cell phones (the towers are all down even if you could get an actual phone working). No cars running. No Internet or computers. No trading or banking (it all depends on computers these days), and no credit or debit cards either- just transactions done in cold hard cash. Half the population might drop dead from sheer boredom, or frenzy at trying to find something to do.
There's only one real problem with remaking this as far as I can tell, but it is a whopper: what's the message going to be? Stopping violence is a good basic message, and can come through unchanged from the original, but phrasing it and relating it to today's political scene- not to mention keeping it from seeming preachy (preachy stuff doesn't tend to go over very well with today's audiences from what I've seen, though I admit I don't know how well it went over with the audience in 1951)- would be extremely difficult. There's so many variables- and a large part of it today would almost have to be telling people to get away from religion, since religious extremism is one of the most-often-used excuses for violence these days. A modern movie studio would have to be very, very brave to put in a message that could be perceived as anti-religion- and I'm not at all certain if any of them have the guts.