I think we should have this clarity for hotfixes as well. I remember this discussion: How long will there be hotfixes available for plone 4.3.x?
What are the intention for hotfixes? The same as the dates above? Always "two major releases before current branch"? Or like @esteele said, Plone 4.3.x will continue to receive hotfixes and bugfix releases until Plone 6.0 is released. and no regular schedule, being a decision made by the release managers?
(After deciding all intentions, it would be nice to have this info as well in https://plone.org/security/hotfixes)