There is nothing implausible about the possibility of ice being buried beneath the surface in these middle latitudes. The real question is how close to the surface and did the GRS detect ice in these locations?

My bet is that the original assumption that GRS found chemically bound hydrogen and not water ice in these middle latitudes remains the most plausible.

Keep in mind that Feldman and Boynton are not arguing that these hydrogen deposits are water ice today. They are speaking about "past near-surface water deposits" and attempting to suggest how the presence of these deposits might alter our view the martian climate in its recent past.