One of the most needed feature that I find missing in packge managers (dpkg, rpm, pacman, gem**, cpan, fppkg etc) is the ability to install more than one version of a package, and create an alternative entry for it or a script that knows how to handle the execution of different versions.
Why do I require such feature you must ask yourself (or want to ask me) ? well lets imagine the following scenario:
You are working on a program with a specific version of a library/tool/compiler/something, and in the next few months, a new version of that thing will arrive, and for now there are beta and rc's on that thing. You wish to make sure that your program works with the new version, but you do not want to move to a new unstable version, or you wish to continue support older versions.
The idea I have will help us work better in such cases. The renaming of a package name does not always helps in such cases (installing in the same directories, conflict of things that they both provide etc..), however knowingly managing different version of the same thing, can help us overcome such issues, and still have the result that we wish to have.
What do you think ?
* All package managers known to me (and me alone)
** gem does support installing multiple versions, but not the way I want it.