I think you might be able to do some research on the trends in prosthetics moving from imitation to functional innovation to stylistic embellishment. Of course this is happening at the fringe and the nature of prosthetics is that they are very custom to the person so the risk in creating the wrong product is little to none. Still, some analogies may be drawn.
Iab, I think it is ok to go into a project with a thesis, the key is to be objective about proving or disproving it. In this case it would be pretty simple to construct a few prototypes, render them up on different subjects and do max diff surveys vs traditional designs with targeted groups of the hearing impaired population in different age, socio-economic, and geographic groups. 3 designs in this more aesthetic forward type direction with 3-4 traditional units in a force rank style survey could yield some interesting results. I would do the force ranks as solo rendering, rendered on a young male, a young female, middle age male/female and so on to see if the participants rank them differently on different genders/age groups vs the devices on their own.