If they're launching a new nexus phone, they better leak it quick because I'm primed and ready to buy the g2x on launch day. I would not be happy if they announced a new nexus phone after my 14 return window closes.
With the rumored availability of Ice Cream Sandwich around June/July--the sort of important upgrade to the phone software that Froyo was for the N1 and Gingerbread wasn't for the NS--it could be LG 2 phones ready to be loaded for dogfooding in Mountainview.
A late April delivery allows for 6-8 weeks of in-house testing and updating before a final release of ICS. Supposedly, ICS will be optimized for dual-core processors, so the NS isn't of much value, it will take a more advanced piece of hardware to fully test the builds. The last deal with Samsung indicates Google isn't giving the Nexus business solely to HTC, and involving a 3rd major manufacturer would be good business sense. The phone having the 3G bands for both T-mobile and AT&T would make even more sense. I think every high-end-loving T-mo customer would buy one of these if they were future-proofed.
I think this will signal the dawn of Nexus 3. Or Nexus LG. Or whatever it will be called.