A different perspective on this (and I don’t disagree with anything said so far) is that HA should only be available for LTS versions. If we can arguably agree on that, work on HA shouldn’t have even started until recently.
Many of the problems with HA are endemic to Asterisk and SIP. There are just some parts of the process that naturally make HA technically hard to do. I’ve believed for a long time that true HA is unattainable because of the way SIP processes calls combined with the way Asterisk implements those controls.
We have workarounds for almost all of the things HA calls for in the Hot-Spare configuration, which works reasonably well. Getting that working reliably could be considered the first step to solving HA’s issues, but for almost everyone, it’s a reasonable approach to HA.