The flagship Land Cruiser has been full-time 4WD since the 80 series, introduced in 1990. I think the only reason they don't have it on all trims of the 4Runner is to push people to pay more and buy the LC250. The LC250 (a.k.a Prado) sold abroad has FT 4WD as well from what I gather.
You may have seen the video where a shock broke on the new Tacoma with moderate offroading. It seems that the 4Runner will be following the same footsteps.