I think some people in this thread are having a hard time differentiating between what THEY want and what actually makes good business sense for Microsoft.
I want 7.8 tomorrow, just like the rest of you. But I understand business and the cold, hard reality is this:
Windows Phone 8 is the future of Windows Phone. The only reason WP 7.8 even exists is as a sort of concession prize for early adopters to placate us until we inevitably buy WP 8 phones and for low-end phones in developing countries.
To release 7.8 BEFORE 8 would make absolutely no sense. It would all the people with 7.5 a reason to delay buying a WP8 phone on impulse, which we all know A LOT of you are going to do. That's bad business.
It would ALSO confuse new customers and blur the line between 7.8 and 8. "Gee why do I want to buy that Lumia 920, this 99 cent Lumia 900 on contract has the same resizable tiles on the screen thingy and it looks 95% the same" Again, bad business.
People are giving the idea that making us wait for 7.8 is going to make us all so mad we're going to jump ship to Android or iPhone WAY too much weight.
That is bullcrap and you know it. If you are bothering to come to a Windows Phone forum, then you like Windows Phone enough to stick around most likely. You're not that damn fickle, and if you are, well... go ahead and go to iPhone or Android, if you think those platforms aren't eventually going to do something that annoys you, you're sadly mistaken.
So Microsoft will do what makes good business sense. Which is to keep 7.8 under wraps and give WP8 as strong a launch as possible. Then when some of the hype over WP8 has faded a bit, they will quietly release WP 7.8 for us.
My prediction is that will be some time around Q1 2013.