Thanks for digging up this 2010 No Action Letter from the SEC - this was published subsequent to when I first looked into this issue.
Based on a quick read, it seems Royalty Pharma successfully claimed a royalty interest falls under the factoring exception - a somewhat tortured reading if you ask me. Likely the SEC was looking for an out here and so accepted their reading.
Based on this, I believe you could now have a publicly traded royalty holding company that would not have to register under the 1940 Act. These No Action Letters aren't always precedential, but I can't see the SEC now moving away from the position they agreed to here.