Here the earliest text has the singular desire, although in theory one’s plural desires can also be fulfilled. The 1888 LDS edition replaced the singular with the plural desires; but since that edition never served as a copytext, the plural reading was restricted to that edition. But the singular is definitely correct since these three disciples who are to remain have expressed a single desire, as mentioned earlier by Jesus:
The critical text will retain the singular desire here in 3 Nephi 28:29.
Summary: Maintain in 3 Nephi 28:29 the original desire (that is, in the singular) since the three disciples had this special desire.