You can now save your diagram as a Gliffy JSON format, both online and in Confluence:

Then import to draw.io via File->Import From:

You can also right click on the Gliffy diagram and select "View Source":

When the JSON of the diagram appears, press the "select" button on the dialog then copy to your clipboard using ctrl/cmd-C. In a new draw.io diagram press ctrl/cmd-V to insert the Gliffy diagram.

Our first alpha of Lucidchart import is also out today (only supporting Chrome, Safari and Firefox, initially). Select your Lucidchart diagram and copy to the clipboard with ctrl/cmd-C:

then paste into draw.io with ctrl/cmd-V:

The Lucidchart import is something around alpha quality, the Gliffy importer is more production quality, report any issues to the support channel appropriate to your product.