Yup, modern CT and a fair bit of MRI is fully 3D imaging where this is less of a consideration. But something like 60 or 70% (anecdotal stats, am an MR physicist) of MR imaging is 2D slice by slice imaging where there will be value for some better interpolation approaches. And even for 3D imaging, non-isotropic scanning (typically thicker slices compared to in-plane resolution) is clinically common to keep scan times short and interpolation could be handy

Interpolation happens all the time in medical imaging data, but it is most often within the image and not across slices. Filling a missing slice between two slices is not routinely done. There is some work where you collect thick slices and attempt to create multiple thinner slices from them.