The retail ASRock X299 ITX board WILL NOT FIT in the Corsair One chassis. We had to modify a daughterboard to ensure that it would work.
To be honest, if you want to go nuts with a Corsair One, your best bet is just to buy the i180 and manually upgrade the CPU to the i9-9980XE. We've actually validated and certified against that CPU. We won't warrant its operation or any damage you may incur by doing the swap, but it can be done and should work fine.
We also have a 64GB upgrade kit for the i180 en route. You can technically buy a 16GBx4 SODIMM kit and it should be fine, but the upgrade kit comes with specially selected ICs and heatspreading tape to guarantee stability.
As for the i140/i160, I don't know what you really gain from switching motherboards. Maybe another 100 or 200MHz turbo? Maybe? You can achieve similar results by manually undervolting the CPU, which could reduce noise in the process.