I think I am way too spoiled by the quick hitch 3pt attachments, such that getting attachments under and out from under the belly of my tractor would be a pain where I sit.
But, over the years, I have thought that a grader blade underneath (like a real grader) would be the cat's pj's. However, there would have to be a lot more room to do anything with it. Maybe the hi mount tractors would work best. Then, a longer wheel base would work better, and more degrees of freedom to move the blade. Pretty soon, wahlah, we have a real grader. Sorry to have rambled on a bit.
Your thoughts were good and it will be interesting to learn what others think.