Forking from T246949
Bootstrap 4.x is now in maintenance LTS as of 2020-05-26, and stays that way till 2020-11-26. Obviously, as 5.x is still not released yet a stable release (there is a 5.x alpha as of 2020-06-16), I'm not going to recommend upgrading just yet. I will file a task for doing so (ideally before 4.x is actually EOL in November), and would appreciate it if that is scheduled into the active work program as things progress. Based on 4.x support cycle, it should be supported for 2.5-3 years, so an upgrade to 6.x presumably wouldn't be needed for a couple of years.
From Bootstrap Long Term Support plan:
5.0 stable release: TBD
4.x EOL: January 2022