Problem/Motivation
The datetime views plugins have wonky timezone support. This needs to be fixed. While most evident in the argument plugins, the filter, and sort plugins have similar problems.
Proposed resolution
Because of coupling with the views architecture, fixing the individual plugins with separate issues is essentially impossible. In addition, a proper fix means moving some backend specific code out of the generic Sql class (date handling in SQL is not equivalent between the supported databases), and fixing some date support in Views itself.
Remaining tasks
Cry, then fix all the things and provide test coverage.
User interface changes
None.
API changes
TBD. It looks like some very low level Views classes may have interface changes.
Data model changes
Original Report
The datetime View Arguments don't take into account the user's timezone. That means that if you make a View that has \Drupal\datetime\Plugin\views\argument\YearDate argument then all users will same events even if the timezone for a user would push certain events into either the next or previous years.
This is probably an edge case for years but for the new arguments in #2567815: Add week, date, and year-month Views argument plugins would be more effect by this.
So if you used the FullDate argument then dates that would be in a different day because of the user's timezone don't show up correctly.
Working on a patch