Even with the PMDG 777 update? I know it was updated for avatar mode specifically so it wouldn't trigger a collision when walking under the wings or wheels so you could do a walkaround..
In that case, and if the plane comes with a detailed interior in the *external* model, then it will work, otherwise you'll not see much, because in Avatar mode, you are still seeing the external model of the plane so, you'll see what the developers of the plane have modeled of the interior, to be seen from the exterior.
To be more clear, you cannot walk as an Avatar in the detailed VC. You'll see only a lower polygon version of what VC parts you are supposed to see from the outside.
That's of course outside our control, it would require an update in P3D to have the Avatar being able to walk in the "real" VC of the plane he's attached to.