Just thinking out loud here, what if CPU’s were purpose built for liquid cooling, made a few inches tall and allowed water direct contact with the walls of the processing unit. Similar to how water runs through an engine block and cylinder heads.
Im no engineer, but as I see it, heat is transferred from the chip to a paste or solder, and then to the IHS (the part you take off in delidding), and then to more thermal compound and what ever is bolted on top of the IHS (air or water block cooler). Imagine a CPU where the water is allowed direct contact with the IHS. I wonder if that would be more effective.
Why hasn’t someone made an IHS that is connected to water lines? Would add an extra install step (de-lid the processor, use new water IHS), but if you are really that worried about a few degrees difference in AIO cooling vs traditional air cooling, you would probably be ok with this.