I won't count on that possibility in a Highlander.
Easily. Several makes have direct fits, and there are some good fit-kits for a double-DIN unit. As a former owner of a car audio electronics store, I still have contacts/friends in the biz, and they tell me that there are some nice entertainment/nav systems that will drop in with a total cost of $1K or so.
Rosen makes an OE drop in, but some research tells me that they're not reliable long term. But, Nav in the Highlander is not needed. My Missus wants Nav, but she wants it in the Corolla. That is an easy fix, with tons of options for that car.