This includes migrating existing packages to Qt6, forcing Qt6 when
a package supports both rather than have USE=qt5/qt6, and last-riting
packages with a dead upstream that are unlikely to ever support Qt6.

Forcing Qt6 was formerly avoided due to poor integration on Qt5
DEs, but Plasma 6 is now stable and LXQt-2.x is not far behind.[1]

The Qt policy page has also been similarly updated.[2]

A removal date is not planned "yet" but we want to make progress
toward that given as the Plasma 6 news item notes:

   Qt5 upstream OSS support ended on 2020-12-08, and LTS
   releases - even with considerable effort by KDE community's
   backports on top - only go so far.

...there is also nobody in neither the Qt nor KDE Gentoo teams that
wants to maintain Qt5 more than necessary and it will slowly fall on
abandon downstream too.

Please prioritize migrating/removing packages that use qtwebengine:5
as it is a constant headache, a security hazard even with backports,
and we'd like to drop it earlier than the rest of Qt5[3]. We also don't
want users to have to compile *both* qtwebengine slots.

On a side-note, the Qt6 migration notes[4] may help a little.

[1] https://bugs.gentoo.org/938702
[2] https://wiki.gentoo.org/index.php?title=Project:Qt/Policies&diff=prev&oldid=1310293
[3] https://bugs.gentoo.org/925718
[4] https://wiki.gentoo.org/wiki/Project:Qt/Qt6_migration_notes
-- 
ionen