In this question, I asked whether it would be possible to make a reentry vehicle that could slow down from orbit and glide to the ground entirely passively. The answers and comments point out several reasons why it is probably impossible for a plane-sized object.
However, there still seems ways to decrease the heating of a reentry vehicle compared to existing designs. For example, the VentureStar project was supposed to use metallic tiles instead of the much more heat-resistant tiles of the Space Shuttle.
What would be the minimal heating a realistic reentry vehicle could hope to achieve?
The vehicle should at least mass a few tons, as the square-cube law seems to make it easier for smaller ones. Other considerations like extravagant reentry duration, awkward shape or limited landing sites can be ignored.