> say I'm releasing a document that say it's gpl v4 and assign all ownership to me. or the FSF goes corrupt.
That would be a voilation of GNU GPLv3 itself (by FSF which is legally wrong). Such a GPL v4 license won't be considered as a later version of GNU GPLv3.
See section 14 of GNU GPL v3:
The Free Software Foundation may publish revised and/or new versions of the GNU General Public License from time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns.
If the later version is not similar (Of course, it is hard to explain this term) to the spirit of the present version, it will not be considered as a later version of current license.
Also, by having 'or later' in the license won't revoke the previously granted permissions.
That would be a voilation of GNU GPLv3 itself (by FSF which is legally wrong). Such a GPL v4 license won't be considered as a later version of GNU GPLv3.
See section 14 of GNU GPL v3:
The Free Software Foundation may publish revised and/or new versions of the GNU General Public License from time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns.
If the later version is not similar (Of course, it is hard to explain this term) to the spirit of the present version, it will not be considered as a later version of current license.
Also, by having 'or later' in the license won't revoke the previously granted permissions.