“Recording deep neural activity via ultrasound can’t be done through the skull, but it can be done by removing a piece of skull and laying the device on the surface of the brain.”
There's an obvious ick factor, but when I think about it, it's not really so bad compared to some of the other things we do to our bodies. I can easily imagine getting a chip of skull replaced with a subdermal device, like you might get a tooth replaced or a pacemaker installed.
To me it's scarier because of the blood-brain barrier and restricted immune response--keeping disease out in the first place is probably more important than usual.