Alas, this believer in transclusion also deeply feels it's important that authors need to be paid, himself included. Perhaps he'd have a better chance to impact history in a meaningful way if he opted to give away for free the works making that case? Very few will have a chance to be exposed to the ideas Ted Nelson promotes: the range of books you suggest shows the impossibility of ever getting a comprehensive look into his view.
More to the point, if he'd opted to open source the code.
In Computer Lib/Dream Machines, one of the systems Nelson describes and lauds is Calvin Mooers's TRAC macro language. Mooers took his IP seriously and defended it seriously. You can read his argument in favor of copyright to protect software in a Computing Surveys issue from some decades ago. Mooers protected TRAC right into oblivion--if even 1% of those who read HN have ever heard of it, I'll be amazed.
David Turner, who has done very important work on implementing applicative languages, similarly protected Miranda, with the result that the major work is being done elsewhere, on Haskell et al.
Project Xanadu is "worse is better" taken to the limit, in which the better doesn't even exist save perhaps as a prototype that you can at best see a short video of. The story of Project Xanadu is a tragedy of seeking funding and resources, exhausting them, and then having to look for more. How much better off would the world--including Nelson himself!--be had he decided to open it up to the bazaar.
There's an open source code dump of two versions on udanax.xanadu.com. "Xanadu Gold" is the most insane codebase I've ever seen -- implemented in Smalltalk but intended for automatic translation to C++.
I've seen a demonstration of zigzag implementing a family tree, I was impressed by its speed and fluidity as well as its ease of use. There is some background and an image of the system here http://crca-archive.ucsd.edu/view_event.php?id=60
A friend of mine says Xanadu got quite a bit further, but failed hard at the end because they'd not bothered to do and keep viable the total end to end use case. Specially, to actually interact with the system and display a document was so hard and cumbersome it never had a chance of being adopted (by pretty much anyone, let alone widely), whatever other problems there might have been with the project.
But the lone visionary has a hard time opening up his/her idea to the bazaar, because then the bazaar gets to mutate the idea away from the shining purity of the visionary's dream. That is, those who most intensely insist on the purity of their idea are the least likely to make a mark. (Steve Jobs is the exception, but he had a company to back him.)
