Firstly, this thread ranks among the more informative and insightful.
From my side there isn't much more to add, only the following.
The mountings, including tsuba were made in a cultural environment that in many ways differ from the world today. Tsuba from the Muromachi and Edo already show signs of a different approach in subject matter and methods of execution and materials used. It would seem natural that contemporary tsuba would differ from their historical counterparts as they are made by artists that are trying to express themselves within the context of their culture and personal experience. The historical tsuba would have been something fresh and new, adding accent to the mountings and uniform. Like all things new, eventually the novelty wears off, it becomes a norm and loses some of the strength of expression. There are exceptions to this rule obviously.
There is nothing wrong in the copying of historical pieces in order to gain a deeper understanding of the mindset and techniques of the historical artist, but even then there will be a bit of the copier expressed in the workpiece due to his interpretation of the item copied.
My opinion is that there will always be a place for modern tsuba and that they will mostly be judged by the way the artist reflects his ideas (and school of thought) within his current environment, something that a blind copy or cast replica will lack.
Regarding the functionality of tsuba and the protection of hand theory (incidentally, has anyone ever thought about it acting as a marker when you draw the sword, pretty much saying 'grip stops here, scabbard starts below', just a personal hypothesis). I am not in a position to comment on the Japanese sword in martial usage, but as I am heavily involved in the teaching of European swordsmanship a close parallel was the cross protecting the hand theory. In reality the instance of a blow striking the cross is very rare (there are situations where it is actively used in offense or defense). It does however serve a a good barrier when your wrist or hand is attacked by someone not stepping offline. I am guessing that the tsuba would be helpful in such a situation , whether by design or convenient coincidence. Trained people tend to step offline to cut to the hands and arms, completely bypassing the cross though. (I should leave this bit for the actual Japanese sword-art practitioners, I believe that includes Ford?).
That aside, in the end as long as there are artists producing unique workpieces regardless of their area of specialization in style or materials, there will be people interested in the pieces because something in it piques their interest or resonates with their perception of art. A given item can mean many things to many people, that tells us more about the collector though and not the artist. In essence some people judge art the same way they judge people, seniority and age counts.
Just my humble bit.
Marius