The Galaxy Nexus was odd timing. It really depends on how close the GS3 comes out compared to the next Nexus phone. History might repeat itself and things will go as they did last year, but I doubt it. Samsung themselves had said that they don't like the long time span between introducing the phone and it being released world wide. I hope with the GS3, they will have something close to resembling a global launch, kind of how Apple handles its launches.
I am pretty sure it will come to Sprint since the GS2 seems to be a good seller for them along with the iPhone. They would be silly to pass it up. Verizon doesn't seem to discriminate as far as what brand phone they offer, they just skipped the GS2 because of the Nexus. It's too early to tell, but I hope we'll know more when Samsung takes the wraps off this beast. I am cautiously optimistic that it's going to be all and end all of all smart phones and will reign supreme as the Android king. After having my Epic Touch 4G for a few months now, I can't ever see myself going back to HTC, and after using a Photon the other day, I can't see myself with a Motorola device either.