It seems as the though the Lexus RX will soon be joining both the GX and the LX in the marque's current three-row lineup. The news of a three-row RX is not surprising as Lexus themselves have previously confirmed back in 2016 that a three-row RX will be offered soon.
According to Japanese magazine Mag-X, the upcoming three-row RX will not have an extended wheelbase, but will ride on the same platform as the same current 5-seater RX. Instead, the three-row RX will have an increased rear overhang, giving third row occupants a minimal sense of space. Meanwhile, the rear window will also be moved back, but the size of the current tailgate will remain the same.
Given that most of the RX's original specification will likely be retained, visibility from the third-row may not be as good given the additional seating. Folding the third-row down however, will supposedly expand luggage space compared to the standard 5-seater RX.
To distinguish the standard 5-seater from the three-row RX, Lexus will supposedly designate the latter with an 'L' badge. The 'L' badge is usually reserved for the long-wheel based LS, and has yet to be used on any other Lexus vehicle in the current lineup. But as mentioned earlier, the supposedly RX L will not have an extended wheelbase ironically.
Mag-X says that the three-row Lexus RX is reportedly going on sale beginning 2018, but will likely be exhibited at the upcoming Tokyo Motor Show in Japan.