Maybe I'm missing something but on /cgi-bin/koha/reserve/request.pl there is a "Change priority" column and a column with 3 downward facing triangles touching a line drawn under them (ie "Set lowest priority"). The former let's you move up, move to the top, move to the bottom, and move down in terms of priority. The latter lets you just move it to the bottom of the priority. Unless I'm missing something obvious, the second/latter one really does seem totally redundant?