We saints row now?
Anyway funny enough it would take a good bit of work to implement since all current pants equipment would need to get an edit to allow this character detail since its not all automatic.
Also it would be exactly like bust size which currently not all gear is equal with what you can call "true bust size", for example take a highlander female with max bust size and see them in the starter gear or a cowl and now put them in the Brand new robe and watch them shrink a lot.
This would also apply to a bulge option if for some reason added and as such it would literally not apply to any gear without edits and even if the edit happens it wont show up at all on quite a bit of gear and only be visible when in your underwear.
Overall its not even worth considering.