Turbofrog

Here's where the logic comes in:
2 x 0.64 = 1.28, similar to APS-H, as you say.
But you're not comparing apples-to-apples if you're using an FF camera to shoot video. Because they have a 3:2 sensor, if you want to shoot DCI 4K, you've actually got a ~1.07x crop factor with any FF camera.
So 1.07 vs. 1.28 is only a 1.2x relative crop factor. Which is of course noticeable, but very small. And given that the GH5S has a much more robust codec than any of the FF video cameras currently available for under $10K, and the new sensor appears to have higher quantum efficiency as well, you can call that 1.2x difference essentially negligible.

Well most other camera take extra crop in 16:9 mode let alone 17:9, so while the crop in GH5S stay the same other camera take a hit on FOV

Here's where the logic comes in:
2 x 0.64 = 1.28, similar to APS-H, as you say.
But you're not comparing apples-to-apples if you're using an FF camera to shoot video. Because they have a 3:2 sensor, if you want to shoot DCI 4K, you've actually got a ~1.07x crop factor with any FF camera.
So 1.07 vs. 1.28 is only a 1.2x relative crop factor. Which is of course noticeable, but very small. And given that the GH5S has a much more robust codec than any of the FF video cameras currently available for under $10K, and the new sensor appears to have higher quantum efficiency as well, you can call that 1.2x difference essentially negligible.

I think it's probably impractical in the real world to expect Panasonic to use an S35 sensor for the GH5. It doesn't fit in with their overall mandate, and it's a hard sell when dealing with their native lenses.
However, a slightly oversized multi-aspect ratio sensor as in the GH2 but with updated sensor tech seems like a much more practical option, and in their best interest in every way. A multi-aspect sensor that goes from 4:3 to 16:9 would be 18.8x13mm, or 18.8x10.7mm in 16:9 mode, or 200mm^2 sensor area.
Compared to standard other formats you get:
Standard M4/3 cropped to 16:9 = 17.3x9.7 = 168 mm^2 = +0.25 stops
Sony APS-C cropped to 16:9 = 23.7x13.3 = 315 mm^2 = -0.65 stops
3-perf Super 35 = 24.9x13.9 = 346 mm^2 = -0.79 stops
 
The multi-aspect sensor uses only a little more sensor area than a regular M4/3 sensor but gives a benefit to 16:9 capture area, is easily accommodated by the mount, and gives users of existing M4/3 lenses the ability to capture 4:3, 3:2, and 16:9 without cropping and taking full advantage of their lenses. Using the new 20MP GX8 sensor, you get native 6K @ 16:9 with essentially non-existent crop.
 
To me, this makes the most sense for how Panasonic runs their business. It caters to their base, and expands their capabilities even further into high-end broadcast and cine land who can now use 6K input footage and edit for 4K output in a similar way to how 4K is now used for 1080p, giving flexibility for PP stabilization and doing subtle punching in and panning. Useful stuff, in general.
 
However, if you live and die by 2/3 stop of ISO or depth of field compared to APS-C or Super35, and firmly feel that that's the difference between the look and feel of something "filmic" or "video-like" I don't really know what to say, and should probably just bow out of this conversation...

I think it's probably impractical in the real world to expect Panasonic to use an S35 sensor for the GH5. It doesn't fit in with their overall mandate, and it's a hard sell when dealing with their native lenses.
However, a slightly oversized multi-aspect ratio sensor as in the GH2 but with updated sensor tech seems like a much more practical option, and in their best interest in every way. A multi-aspect sensor that goes from 4:3 to 16:9 would be 18.8x13mm, or 18.8x10.7mm in 16:9 mode, or 200mm^2 sensor area.
Compared to standard other formats you get:
Standard M4/3 cropped to 16:9 = 17.3x9.7 = 168 mm^2 = +0.25 stops
Sony APS-C cropped to 16:9 = 23.7x13.3 = 315 mm^2 = -0.65 stops
3-perf Super 35 = 24.9x13.9 = 346 mm^2 = -0.79 stops
 
The multi-aspect sensor uses only a little more sensor area than a regular M4/3 sensor but gives a benefit to 16:9 capture area, is easily accommodated by the mount, and gives users of existing M4/3 lenses the ability to capture 4:3, 3:2, and 16:9 without cropping and taking full advantage of their lenses. Using the new 20MP GX8 sensor, you get native 6K @ 16:9 with essentially non-existent crop.
 
To me, this makes the most sense for how Panasonic runs their business. It caters to their base, and expands their capabilities even further into high-end broadcast and cine land who can now use 6K input footage and edit for 4K output in a similar way to how 4K is now used for 1080p, giving flexibility for PP stabilization and doing subtle punching in and panning. Useful stuff, in general.
 
However, if you live and die by 2/3 stop of ISO or depth of field compared to APS-C or Super35, and firmly feel that that's the difference between the look and feel of something "filmic" or "video-like" I don't really know what to say, and should probably just bow out of this conversation...

I think it's probably impractical in the real world to expect Panasonic to use an S35 sensor for the GH5. It doesn't fit in with their overall mandate, and it's a hard sell when dealing with their native lenses.
However, a slightly oversized multi-aspect ratio sensor as in the GH2 but with updated sensor tech seems like a much more practical option, and in their best interest in every way. A multi-aspect sensor that goes from 4:3 to 16:9 would be 18.8x13mm, or 18.8x10.7mm in 16:9 mode, or 200mm^2 sensor area.
Compared to standard other formats you get:
Standard M4/3 cropped to 16:9 = 17.3x9.7 = 168 mm^2 = +0.25 stops
Sony APS-C cropped to 16:9 = 23.7x13.3 = 315 mm^2 = -0.65 stops
3-perf Super 35 = 24.9x13.9 = 346 mm^2 = -0.79 stops
 
The multi-aspect sensor uses only a little more sensor area than a regular M4/3 sensor but gives a benefit to 16:9 capture area, is easily accommodated by the mount, and gives users of existing M4/3 lenses the ability to capture 4:3, 3:2, and 16:9 without cropping and taking full advantage of their lenses. Using the new 20MP GX8 sensor, you get native 6K @ 16:9 with essentially non-existent crop.
 
To me, this makes the most sense for how Panasonic runs their business. It caters to their base, and expands their capabilities even further into high-end broadcast and cine land who can now use 6K input footage and edit for 4K output in a similar way to how 4K is now used for 1080p, giving flexibility for PP stabilization and doing subtle punching in and panning. Useful stuff, in general.
 
However, if you live and die by 2/3 stop of ISO or depth of field compared to APS-C or Super35, and firmly feel that that's the difference between the look and feel of something "filmic" or "video-like" I don't really know what to say, and should probably just bow out of this conversation...