Let me take my insane idea and validate it.
Mini ITX MB + SFX PSU. GPU irrelevant.
All watercooled on custom loop.
I can see i would potentially do 2x 360 rads in top/ bottom. I can assume not very thick, max 30mm + 25mm fans but at least 20.5 mm + 15 mm slims. That would dissipate some 3-400w...