I don't see @Ello as a "Facebook-killer." Certainly not until it moves past the beta (or maybe alpha) version it's in now. Facebook has spent too much time and money and influence getting itself wedged into too many other online systems, like an invasive vine, and too many people are locked into its ecosystem far more deeply than they ever were with, say, MySpace. Right now Ello is a curiosity, a slightly-less-useful Tumblr alternative without (as yet) any way to like or repost anything. Ello is benefiting from general distrust of Facebook galvanized by its recent fake-name purge, but so far it's just someplace to to flee to, not to approach on its own merits.
With all its flaws -- and there are so many -- and the open and blatant way it harvests your info for sale, Facebook still fulfills users' needs, and unless Ello can do the same it will not survive on its own as anything more than a small social network with a passionate but largely walled-off community. Google had way more resources and name-recognition when it started Google+ and it hasn't even approached Facebook's popularity.
The current attention and gold-rush mentality is good, but Ello needs their proposed "Love" system in place, and some way to repost posts, and a messaging system. All those are in their list of someday updates, but they're utterly necessary to even begin to take on Facebook and bare minimum for a decent Pan.
I'm sorry, I dropped into "Hook" for a second there. I'm better now.
Personally, I'd like to see Ello keep the outcast, LGBTQIA, first-responder feel it started with and stick with the under-the-radar, counterculture feel it has now, but with the VC funding it really can't. I have no idea what it might become. But Facebook will still be there, arrogant and brightly-colored as ever.