I think this is where we need to make a distinction. I don't feel the Nexus 5 is based off the G2 at all...no rear buttons, slightly smaller screen, the cameras and flash are in completely different places on the back of the phone.
This phone seems to be going back to the pre-Nexus 4 way of doing things. A device unto itself, not based off another device in the pipeline. I may be wrong, but isn't the Nexus 4 the only Nexus actually based off another device? I don't think the N1, Nexus S, or Galaxy Nexus had sister phones, correct?
I'm really excited about this Nexus. Hopefully Google doesn't prove me wrong, but I really think this is going to have all the bells and whistles. Big screen, great camera, decent battery. All in a beautiful package that allows you to tinker until your heart's content. You know, since the carriers have all decided to embrace the locked bootloader crap.
I could be very wrong, but I thought the Nexus S was based on the Galaxy S1 (thus the S) and the Galaxy Nexus was based on the Galaxy SII (thus the Galaxy, I guess?), no? Again, not sure.
In any case, I think the Nexus 5 could be considered based on the G2 even if it's dramatically different. The Nexus 4 was based on the G1 and was pretty different, too, though admittedly not as much so as the speculated G2-to-Nexus 5, but that may be because the G2 is particularly unique (back buttons and all).
And I'm with you -- I'm as hopeful as you are about this year's Nexus. The main reason I feel hopeful this time around is because of the Nexus 7 (they even got the launch right). Google really gave it everything it needed and did so with only a moderate price bump. I hope they repeat this for the Nexus 5.