there have been couple of posts I have seen where folks are looking for nuget packages that are now unlisted and don't have an idea on how to proceed
1. there should be an option for the owner to specify details on why the package was unlisted and any pointers to the new package or workarounds.
2. If owner still wants to display it in the search results so that customers can know about the details.
I would say basically you're requesting a 'deprecate package version' feature, which works differently from unlisted packages since it shows up on the package page in the versions list (at least I assume so - where else would you logically put it?). Maybe you need an extra step to see deprecated versions. And you can't see them anywhere else?
I can certainly see the applications for telling people 'we unlisted this package version because there was a security bug', or 'it contained unintended breaking changes'.
Is it a good solution to the original problem where people are confused about why they can't find a specific package version? I agree it solves a problem (knowledge) for them, but feel some skepticism of value:
-I suspect it creates problems for the author of the package in that it feels like a weaker way of discouraging people from using that package version. I imagine that discouragement is a high goal.
-Does it really cause the end user to handle their problem any better to say 'yes that version was unlisted because X than yes that version was unlisted?'
-Won't the package owners be blogging about it or something already, if they want you to know?
Going to leave this without a milestone for now.
Definitely sounds like something the client could be involved in too. For example, when we do any install operation, we can check packages for deprecation (or do it in the background on solution open, etc.). Then the client can say: "You are using a deprecated version of jQuery. The recommended version is ...".