Well for some. Google has been using liquid cooling to racks for decades.
> Bringing liquid cooling to the racks likely has to be one of the biggest challenges with this whole new HPC/AI
Are you sure about that? HPC has had full rack liquid cooling for a long time now.
The primary challenge with the current generation is the unusual increase of power density in racks. This necessitates upgrades in capacity, notably getting 10-20 kWh of heat away from few Us is generally though but if done can increase density.
HPC is also not a normal data center but also usually doesn't have the scale of hyperscaler AI data centers either.
> The liquid-cooled AI racks being used today for training and inference workloads almost certainly have far higher power output than that.
75kW is a sane "default baseline" and you can find plenty of deployments at 130kW.
There's talk of pushing to 240kW and beyond...
(Bringing liquid cooling to the racks likely has to be one of the biggest challenges with this whole new HPC/AI datacenter infrastructure, so the fact that an aircooled rack can just sit in mostly any ordinary facility is a non-trivial advantage.)