I think you are referring to slow-wave enhancement wrt "shorten sleep cycles", which probably isn't the right way to look at it.

We've been developing slow-wave enhancement for the past 4 years using auditory stimulation.

The problem with using focused ultrasound to accomplish this (I believe), is that the focal point creates heat, and I don't believe we want to be consistently creating hot spots of neurons in the brain.

Other methods (acoustic, visual, haptic) have proven efficacy by "tricking" the brain into increasing slow-wave delta power, and tMCS (magnetic) coaxes the neurons into a slow-wave pattern - though this is not realistic outside of a clinical setting atm.

Absolutely there is tons happening in neuroscience (lots here in Sydney, Aus), and focused ultrasound has it's place, but as a daily use, I'm not there with it yet.

For treatment of depression, for diagnosis, etc, absolutely. Though in depression treatment, SAINT protocol tCMS is very impressive.