This question was triggered by Szabolcs excellent questions and answer here and here. One of the open questions is why the paclet manager obviously keeps older versions of paclets installed even though loading will always only load the newest paclet version. One reason could be that a newer paclet could not be compatible with an older Mathematica version and the loading mechanism I think will load the newest installed version which is compatible with the Mathematica version that loads the paclet. Another reason could be that you could explicitly uninstall the newest version to fall back to an older version.
There are the currently not supported functions PacletDisable and PacletEnable which seem to do what I think would be very useful: switch between different versions of the same paclet.
So my question is whether anyone knows what the concept of the paclet versioning is and which functionalities for it are available. One thing I would be very interested is whether and how it would be possible to switch between different installed versions of the same package. Another functionality which would especially useful during development would be whether it is possible to load two versions of the same package into one session (using e.g. differing contexts) for comparisons etc.
