My experience with these pens was actually using them before CAD was fully implemented in the 1990's. (I still have a few of them around in various conditions). I haven't examined the newer ones, but doubt that they have changed much unless the threads/mounting has been changed. I think that one would be able to accommodate the vintage nibs and maybe the new ones in a fountain pen.
I believe the challenge will be aesthetics because of the industrial look of these nibs. I think that a nib cover may be in order and, because of this, one of the longer drafting type rapidograph nibs might work best. Have you ever used one? If the nib were exposed it seems to me that it would be a relatively easy task (but doubt its acceptability to you). I will try to look further into the new versions and will need to try a couple of ideas in the shop before I could say definitively if I could produce something that I think is acceptable. I don't sell custom pens as a business, but build them for the challenge of doing it and because I like pens. I am a retired engineer and generally only do one-offs for my own collection and to pass down to my family.
I have worked with metal, acrylic, wood, ebonite, buffalo horn, cebloplast, micarta, and am trying to learn (with only limited success) urushi lacquer. Which size, style, material, filling system,etc. do you prefer? Do you know the line size of your Visconti?
I believe that there would be little difference in construction of this pen and a conventional one except the section and nib (with the nib cover and filling system accommodation being the biggest challenges). It may be that you can procure a custom pen of your preference and have an interchangeable rapidograph section/nib made for it, If this were feasible, do you have one or two already in mind? I think any number of makers could do this, so feel free to pursue this with others. The interchangeable section is one of the ideas that I intend to investigate. FYI, most of my section to barrel connections use M 10 X 1 threads.
As I am doing this just for an interesting challenge, I could not commit to my success, time schedule or cost at this time. So please proceed with any other sources that you can. I will keep you posted on what I come up with. And will you please keep in touch with me (either on this forum or by PM) as well?
BTW, I would love to see photos of the Visconti disassembled, but don't do this if there is any risk at all of damaging it. I also collect vintage pens and certainly wouldn't want to see it harmed.
Please excuse the length and rambling nature of this post,