Previously I tested 'Live' ISO this time I tested in installed VBox from ISO 2543 (x86_64). Everything above seems to have been fixed as best I can tell. So good. Very good.
The KMail issue or issues Y'all know about by now and you should also know that the "Plugin library 'grantlee_defaulttags' not found" issue exists in Akregator as well. Whether this is a blocker I should leave to others as I am prejudiced against KMail myself. I am inclined to say that "broken KMail can't be a blocker because KMail always seems to be broken somehow or other for some users."
Another thing I noticed that should have been noticed and reported previously is that SimpleScreenRecorder has a H.264 codec selected by default. This can't be right because we don't have that codec on a default system so we should change that to some know working codec. For me in VBox using VP8 codec worked for instance. I do not consider this a blocker.
I know Colin keeps having trouble with VLC but for me it has been and continues to work just fine. Since the default in file associations is mpv and as far as I know there are no reports of it not working I don't see this as a blocker at all.
So I'm a failure. I just haven't found a last minute blocker. I would have no choice but to vote GO for this ISO.