I'm really hoping for something better than the 20Mp sensor (assuming it performs like the one in the GX8).
If I had to guess (and that's all it is, a guess), I believe that the 20mp sensor in the GX8 is a Panasonic sensor, not a Sony sensor. Panasonic, to the best of my knowledge, has never used a Sony sensor in one of their m43 cameras. Many believed that the sensor in the GH3 was a Sony sensor, but further research has show it is indeed a Panasonic sensor.
I too agree that the sensor in the GX8 isn't all that impressive. I personally would've rather had a next-gen 16MP sensor with even better dynamic range and low/high ISO performance, compared to a 25% bump in resolution (something that those who actually print their images will likely attest really isn't necessary). But, we know how spec-sheet photographers have a hard-on about how good a camera looks on paper, and 16 is a smaller number than the 24 from Sony or 28 from Samsung's APS-C cameras, and a MUCH smaller number than Sony's 42 or Canon's 50 in their 35mm cameras.
If I had to guess, I'd say the 20MP sensor in the E-M1 II is a good performer, likely a marginal bump over the current Sony 16MP sensor's performance. However I don't see it as being "ground breaking", and it will likely be the features of the E-M1 II that will be the big selling point (larger EVF maybe, hand-held hi-res, 4K video, slow-mo 1080p, improved 5-axis IBIS, etc.).
Time will tell...