This Gear Swap during Greater Rifts exploit provides an unfair advantage in that the Boss Killer can act as a 3rd support during the rift, in providing buffs through Oculus ring / Toxin gem etc.

Together with the Gear Swap during Greater Rifts exploit by using macros to quickly swap paragons in Vitality and main stat (which we still haven't heard anything about being fixed next season/patch, to lock paragons, same as gear), the endgame high end pushing revolves around using so many unintended exploits to gain unfair advantages.

Gear Swap during Greater Rifts Steps

How long this Gear Swap during Greater Rifts exploit will last, we cannot surmise, but checking the patch notes will tell you, if you look at the above warning signs.