I think heatsinks still needed for single phase.
The big problem still is how u gonna cool the liquid... You still have to deal with the same amount of heat to remove. Immersion is good for 2 things.
1) Have a buffer zone. If u generate heat in bursts, like typical computing, gaming, etc where you run it at max power for short times and not 24x7. You only have to deal with the average. - Not applicable here.
2) Channel heat elsewhere where you can exchange it more efficiently.
I was thinking a system more similar to the asicminer system, but i beleive that involves a sealed tank, and still requires either circulating the liquid through a radiator or having a peltier cooler for the gas state