The release is now out and XLSForm Online has been updated! Thanks to all who have participated in this big lift.
As I was verifying the release, I noticed another change that I had not explicitly thought about. As described above, the XLSForm filename is no longer used as the root node name. However, it is used as the default form title and form_id but it is no longer validated to ensure that it is a valid XML element name. That means that form_ids with spaces or special characters are now possible.
I have verified that Collect, Central, Aggregate and Enketo can all properly handle form_ids with spaces and special characters. I can't see any limitations on the instance id element described in the ODK XForms spec or in any other documentation so I believe that this is ok but I wanted to flag it in case anyone has concerns.