Windows 8, Phone 8, Phone 7.8
Microsoft has annouced about general availability of Windows 8 on 26 Oct 2012. I have been playing around with dev preview, then consumer preview and now release preview and look forward to the final release. I do intend to update my home PC with Windows 8.
While there is no specific annoucement on Phone 8 or the update for existing consumers to Phone 7.8, I would guess that Phone 8 should release around the same time as Windows 8. The upgrade from 7.5 to 7.8 will probably happen after that, in an attempt to push some of the existing consumers to Phone 8.
[Edited 20 July] Updates on dates of Phone 8, Office 2013 etc