For normal wetsuits I dont see the need, as one can just take the top down and thats it - take a pee, easy.
And others dont mind doing it in the suit.
But for the winther suits (5/3 or 6/5/4) when used at winthertime - it is a major issue for some, as you can not (wont... as your session will be over...) take the top down in snow or cold maybe even freezing conditions.
So here it would be great
Although, many ride with drysuits in cold weather here anyway, where you dont have this problem (front zip or pee zip)
So I think most kitesurfers who use wetsuits at winthertime, rides more "intense" for a shorter period of time.
And those who wants longer sessions, use a drysuit.
Thats what is seen around here, and you can choose yourself what you want
For suits used "away" from winthertime, I can not see how the higher price/process/annoying zipper could be justified - but maybe thats just me who think so ?
But that could explain why there are no, or very few, wetsuits with a pee zip.
Peter