There is some discussion started on
bug 348099 about how many previous versions PDE should support development
in. Currently we have full development compatibility going back to
3.1, with limited support for 3.0 plug-ins. One suggestion is to
only support n-2 versions, another is to support going back to 3.3 when
the last change to the manifest structure occurred.
Please add your thoughts to the bug
or respond to this email.