If we got a 70 or Prado in
If we got a 70 or Prado in the US, then I would be okay with the 4runner going unibody, as long as that 70 or prado was reasonably priced like the 4runner. 'Froaders like us would not buy it but most 4runner owners are soccer moms and mall readers anyway.
As for the engine, the reason it hasn't changed is because the reliability beats almost any engine of its type, and any redesign might mess that up.