Just finished watching that. Long video, so brief summary:
The problem stems from the pump/block being the highest point in the loop. This would be a problem whether using a regular AIO, modular AIO, or a full custom loop. There's nothing wrong with mounting a radiator at the bottom. But air needs somewhere else to go besides the pump and/or block(s). With a modular AIO or custom loop, the solution is pretty simple; add a 92mm radiator to the rear panel (tubes exiting at the bottom). Air will now collect at the top of this radiator.
With a regular AIO, there is no solution. If mounting the radiator at the bottom, it's best to pick one with a pump which can be run dry (Asetek was specifically referenced) to avoid killing the pump. The AIO will likely run louder, and performance will be lower, and it may still breat down as internal temperatures rise and plastic begins to warp. But it's better than running an AIO with a pump that needs to be under liquid.
Not hugely relevant to NR200, but if you're mounting a regular AIO radiator at the front of the case, make sure the tubes exit from the bottom. This is less a performance issue, and more a noise one. Also make sure the other end of the radiator is the highest point in the loop (this is where you want air to gather).