Papyrus 4.2.0 will provide improvements on the following topics:
The org.eclipse.papyrus.extensionpoints.editors plugin is now called org.eclipse.papyrus.infra.gmfdiag.extensionpoints.editors.
There is no migration, files created under papyrus 4.0.0 or 4.1.0 can be opened with papyrus 4.2.0
You may also look at the API Evolution Report.
Papyrus 4.2 continues to support modeling with the following standards as part of the simultaneous release or as incubation additional component (*):
The Papyrus Industrial Consortium continues to federate the development efforts on Papyrus in addition to facilitate the coordination of the Papyrus developers community in order to meet industrial needs.