More Avacyn Restored spoilers trickling in throughout the night:
I suppose it makes sense for them to push this flicker theme with all the Undying and ETB effects going around. But it's weird that they're pushing it in both white and blue. Sure Momentary Blink a blue splash, but that was a Time Spiral card and that was only flashback. Still, only 30 or so spoilers into the set and this effect has already popped up a number of times. That being said, I think Ghostly Flicker is definitely limited playable. It's a catch-all protection spell for your permanents as well as a combat trick all on top of Flicker abuse at instant speed. I like it a lot and I think it'll see lots of play.
(Note: Much like Cloudshift, it can only target your own permanents and not your opponent's. This is something I missed when I was reviewing Cloudshift. It's not just "strictly better" like I [wrongly] stated before.)
Since Cloudshift and Restoration Angel are already occupying much of this design spice, I think the question for Ghostly Flicker becomes which non-white deck can we abuse this best? What can this do (in blue) that the others can't (in white)? From there I think you have to begin looking at artifacts and lands. Tolarian Academy? Tumble Magnet? Sphere of the Suns? All of the above?
Cube Talk: That being said, I probably won't be adding this to my Cube. Yes, it could cheat morphed creatures into play like the best of them, but I think part of designing a Cube is giving each color its own identity. There are plenty of ways for other colors to flip morphs (Safe Haven, Undying Evil, championing a creature, etc.), but I want to keep the Flicker/Oblivion Ring effect squarely within white's color pie.