Vertical Faces, Walls & Real World Instances
MSCAD needs to have the ability to have vertical faces and other solid objects, put into the drawings via points, or manual methods. The Tin needs to be able to recognize these objects, or at the very least treat them in a manner that is to be ignored without cuasing error. The Tin could just run right into a solid object (such as a water channer shear retaining wall) then move along the face of the object if need be befor picking up the next survey point. This would make area calculations potentially easier. Especially if you can then set your polylines to the wall popints and ignore, say the existing area beyond the walls. This feature would also help out anyone who is dealing with structures, culverts, water ways, even terraced areas.
Ron Mak commented
I usually do the small offset and it is a work-around but can result in strange results (e.g., spikes to phantom points). Even two parallel 3D lines (top edge of a retaining wall) does not process properly with TIN edges crossing over for some bizarre reason.
Could you not just offset your tin points by a very small amount? This works for me. I don't think your going to see this in a CAD environment, its like dividing by zero for them.