Just an idea that occurred to that since updatesite zips and our old dropin compatible zips has same layout users keep trying to put them into dropins folder.

Could would add a "NOT_FOR_DROPINS" with text explaining this an updatesite and (or at least) a readme or instructions file outlining:

"This file is an Eclipse update zip to be used from within an Eclipse installations update manager.

Do not unzip this zip into Eclipse directly nor into its dropins folder - it will not work.

Use the Eclipse P2 Update Manager UI to perform the installation."

Just a thought after seeing multiple users asking why their installation does not work anymore.