I just tried out cloning with beta 3. At first sight it went great, the VDI file naming now works much better than before. Time estimates are as wonky as ever, but I appreciate that that's not seen as a priority.
I also checked to see if you had implemented my suggestion made here, to preserve the main DMI signature in the clone by setting a new <ExtraData> item matching the original VM UUID. To my surprise I found that the entire <ExtraData> section had been eliminated from the clone xml.
Isn't this a bug? It would mean that all "VBoxManage setextradata ..." effects from the original are lost from the clone.
Or did the cloning process somehow determine that all my existing <ExtraDataItem> lines were obsolete?