I am guessing it is coming out around the time WP8 comes out? I do want to get it early though, because I can update it, play around, and get the new phone. Mine is 1st gen, so it is just in time to renew my contract. I am not sure if 1st gen can upgrade either, I hope it is.
It looks like every WP7.x device will get upgraded to 7.8. I don't think you have anything to worry about.