From the Debian Policy Manual:
An orphaned package is one with no current maintainer. Orphaned packages should have their Maintainer control field set to Debian QA Group packages@qa.debian.org. These packages are considered maintained by the Debian project as a whole until someone else volunteers to take over maintenance.
The above is official policy. It references the Debian Developer’s Reference, which is considered non-normative but best practice. The relevant sections are 5.9.4, Orphaning a package and 5.9.5, Adopting a package (I note that the situation with usb_cam may have been considered by Debian to be package hijacking). Also relevant is 7.4, Dealing with inactive and/or unreachable maintainers.
I think the Debian policy and procedure sounds good. It requires a bit of infrastructure work, but nothing too burdensome. It relies on having a known “QA group” but I feel that the OSRF could fill this role.