When the first BX came out, Kubota had not considered cruise control. Quite a few of us e-mailed Kubota re. cc for the BX, and as an afterthought, they designed a cruise control that could go in that slot (Kubota Parts item No. BX7340). There are others who have put control for rear remote in that slot. When later models came out, the cc was redesigned and put in a reasonable location.
I'm not sure about this, but it seems like I read somewhere that when Woods first came out with the BH6000, they moved the seat belt to that slot when doing the seat retrofit. Again, this is one I vaguely remember, and am not at all sure of the correctness. In any case, that was not what KUBOTA originally had in mind for it.