I think his intent was that the sharing happen through an one to one exchange between trainzers. For example, I upload the files to Google drive possibly with a password and then send you the link and the password via email. Not broadcasting the link to the world. I imagine this was done to prevent users of illegal copies of Trainz from getting hold of the files. Sadly Trainz has always been heavily pirated software and this is in no small part due to the many websites that offer content without verifying if the downloader is a legitimate user of Trainz.
He did not want it uploaded to the DLS because at the time many creators took issue with Auran's terms that you had to agree to when uploading content to the DLS. As far as I know those terms have not been relaxed so I would say it is still a no to upgrading it and putting it on the DLS without his permission.
What is odd to me is that although I had all his stuff in TRS2004 and it was very nice by those standards of the time it would be extremely dated today. I understand that it is unique but why hasn't someone like RRMods or Jointed Rail created the same stuff if it is so popular?
William