BZ/RZ wheel base is the same size as the current highlander. The TX/GH will probably have to stretch some proportions to accommodate a 3rd row that adult humans with legs will want to be in, unlike the current RX-L, and to a degree the current highlander. Whether they make rear/d pillar area upright, or they actually go full extendo is up to TMC. However that being said those 3 row CUVs during EV day, seem like both will happen.
Side note:
The characteristic trait of the highlander is the armrest in that Akio picture; the only vehicle that does the fixed armrest with a sliding top is the highlander special. That interior is a highlander repurposed for testing. Remember the TGNA-K platform will underpin the RX, TX, Highlander, GH (the list goes on).