Don't hold your breath
Rest assured, dear children of the corn, no, there will be no further updates. Ever? Never. 7.8 is a one-off Miss Congeniality consolation prize. One and done. And I know, because MS did this to me, and thousands of other loyal Windows Mobile users in 2010. MS said that we were valuable "Windows Phone Classic" (i.e. WinMo 6.X) legacy users and that "WP Classic" would continue to be developed and sold on lower end handsets in poor countries and development would continue in parallel to WP7. HA! Well that, of course, never happened, and worse, HTC HD2 handsets that could have been upgraded to WP7 by MS never were. The rest of us maxed out, if we were lucky, at 6.5 and only a handful of remaining models were sold with 6.5.3 that had more of a touch friendly interface, less reliant on the metal stylus. That is unless you somehow updated the OS yourself. But otherwise no, once 7 was announced, no further official updates or bug fixes came out and the MS 6.X App store just withered on the vine. Only a handful of mainstream, commercial apps were really written for WM6.X anyway, and with 7 it was even less so. The MS 6.x Marketplace was totally shut down by MS a few months ago, in fact. So no, I wouldn't bet anything that we will see anything past 7.8. Sad but MS can't be trusted to do anything else, not after the 6.X debacle.