I do hope there's a successor, but...the GX7 is not that old, it had a brand new sensor when it was introduced - so little hope of a better one in a new model - and at the $399 I just purchased mine for, I know that there isn't a better camera on the market.
The only thing that I think the GX7 desperately needs is Auto ISO in Manual Mode. It's embarrassing that it doesn't have it (and that it wasn't added in firmware), but to me that's it's only glaring flaw. Very much looking forward to taking delivery of mine.
Honestly, I think getting hopes up for a GX8 is too early, and won't necessarily lead to good things. The GX7 is still easily competitive with the best cameras in its class (A6000, X-E2, E-M5), and even after throwing every feature they could at it, I don't know if it sold particularly well. It was probably too expensive at launch, but the body is a very clear step above competitors like the A6000 that launched a cheaper price, so I don't really know if there's an alternative there. I wish it was weather-sealed, but M4/3 needs more weather-sealed lenses before that's a must-have feature. Even one weather-sealed normal prime (in the 17-25mm f1.8 range) would make a huge difference to the desirability of weather sealing for me.