In the early days of the 3DR Solo, they added something akin to retrace path as an additional failsafe but ended up disabling it shortly after. The problem is that GPS to this day is not that accurate. Under the best conditions, the accuracy is only to about a six foot bubble. This might be ok if you're in a wide open space but the accuracy is not good enough to say, back out from a stand of trees. Additionally, GPS accuracy is going to be much less when the GPS signals are blocked by the trees themselves.
It simply isn't technically possible (yet, anyway) to record a path accurate enough for something like retrace to be feasible.