This new format (package) probably was introduced to keep XMLs small and simple while introducing all this new tracking stuff. Latter can create huge amount of data.
This is also valid for other effects data.
So it’s not a real change of format – the XMLs are the same format – but an extension to keep data collections together.
To get a standard XML version export a 1.9 one or just drag whatever you need – project, event, library etc – from the FCP browser either to the Desktop, TextEdit, BBEdit or similar app which supports drag’n drop from clipboard.