Dont overthink it. In engineering I use the KISS philosophy.. Keep It Simple, Stupid!. Im thinking you wont be rotating this very often, but it will be nice to have that option occasionally, right?. If youre going to use the mount you showed previously, I would simply make 2 round pieces of whatever material you have laying around big enough to completely encompass the ceiling mounting base of the mount. As others have mentioned, get a lazy susan style swivel to mount between these 2 disks but also drill a center hole and through bolt these together with fender washers and a Nylock nut to support the vertical loads. you can adjust the squeeze on the lazy susan bearing this way as well.