Hypothetically, even if the GN was a Verizon exclusive forever in the US, it would only affect Sprint users. T-Mobile and AT&T users could just import the GSM version.
Sent from my Google Nexus S
The issue I think Google/Sprint are making with the Galaxy Nexus is that Sprint already said WiMax is going down. They don't have an LTE market up yet. I know Sprint is still selling WiMax phones. Google stated it was only making 2 phones, LTE and HSPA+ "4G" devices. Considering Sprint's LTE isn't on the same frequency as Verizon's, I don't think the the verizon model will work on Sprint's LTE network whenever they get it up.