Sorry this isn't 100% true. A mesh panel is more airflow restricted as a classic vent hole patter like on the C4 even it is done over a smaller area (https://www.pugetsystems.com/labs/articles/Effects-of-Grill-Patterns-on-Fan-Performance-Noise-107/). See the GPU thermals on T1 vs A4. Yes the thermals are the same level, but the A4 has a much smaller vent hole area. The big advantage for mesh is noise reduction (because of its restrict level), cheap manufacturing and it work like a budget dust filter. I personal does not like the look.
For the GPU water block you are right. It requires a narrow one like the Watercool Heatkiller or a special one with fitting port under the GPU like the new EKWB slim one.
The final version will have the same capabilities for the radiator and GPU as the M1 + extra 280 radiator support on the side attached AIO bracket. So on max out you can fit a 240 radiator on the bottom + 280 radiator on the side.
To be fair the U9S is not made/big enough to cool the 3900X proper. On a different motherboard you can mount the C14S that will be a bit better. Yes two 120mm fans on top would result in better air cooled temps but would also add another 0.8L to the case.
The case width is not big enough to support 280 AIO at the bottom + Lian Li clips.
For the possible final version I will make the inverted layout to default and remove the flip feature, because there is no use case where the default orientation is better.
With your hardware it will be like a walk in the park cooling the CPU very silent. For the GPU you have to use a aftermarket heatsink to reduce temps and noise.
Yes you are right - it would be the smallest existing case with this feature.
Nearly yes, some mm are missing. On a possible final version the area above the motherboard will be smaller and the lower bigger. The GPU will have a higher level and will be covered even more. I did also some tests with covering the vent holes in this zone completely and that changed not that much. The GPU does not create enough pressure to move enough air out in these zones. It is easier for the hot air to be sucked in by the radiator. The real advantage of these holes will be achieved by using a deshrouded GPU with outtake fans.
If the C14S would fit on my board in this case I think I would agree, but not for the LP heatsinks on your list.
