Well, now being pretty far into the DayZ SA Alpha, and no current design or work known of about thigh rigs and holsters is a bit unsettling. I thought it would be a pretty good idea to introduce my thoughts on implementation to them in-game. Lets start off with why it can be necessary, For one in real life it is highly unpractical to use a chest holster due to concealment and safety, more people use the holster that goes under the armpit(sorry for lack of actual name).Besides these practicality issues lets go into concepts of how the items said will work in-game. The Thigh Rig or Thigh holster can go on either left or right of your thigh allowing for more carry space( 4-6 slots).The character can have an assortment of ways to put it on, the point is you can have a holster and rig on at the same time(one on left and right leg) . However the Thigh holster can hold 2 slots(the firearm does not count for slots the 2 slots are for magazines) in competition for a regular inside the waist or regular hip holster that only holds a firearm. This will chip off each item into sections; concealment and capacity. While the Thigh holster dominates in capacity it may take a blow from the concealment you get from either of the two other holsters(inside the waist has utter concealment). Inside the waist holsters cannot be seen by a robber while in the victims inventory. My final reason is that while you have a tactical vest you can also run with the Holster and Thigh rigs.
PS: Sorry this was a very rushed paragraph, forgive me for spelling errors and missing other valuable points. Feel free to wright them in the comments.