You can't call 1-800-DELL to order your hardware and set it up next week.
Also, at this moment of time, most hardware has been designed with air cooling in mind. This means we are often spending a lot of time to remove bulky heatsinks and disconnect fans. Big power connectors that are fine for air cooling (there is plenty of space to spare with air cooling) might be in the way to stack hardware in a density that would be possible with immersion cooling.
The advantages far outweigh the disadvantage already now. But one can only imagine the true potential once hardware manufacturers discover how much smaller and more efficient they could design their hardware with full immersion cooling. Luckily for us, Intel and other manufacturers are looking ahead and start to offer hardware in denser form factors (ie. Intel® Xeon Phi™ DFF cards).