I wouldn't be surprised if it takes years for the phase-out, if it ever gets phased out at all. There is a particular type of organizational culture that believes having the "big" option for a productivity tool is the best option. AzDO feels like the "big" option. It is quite customizable and can emulate (and in some areas surpass) GitHub's functionality, but at the expense of having more knobs. To me, AzDO feels like the inside of a space shuttle, but I'm certain that this complexity is seen as a strength to some orgs.
In CI-land, though, I think GitHub Actions and Azure Pipelines fates are much more closely intertwined. The Microsoft-hosted runners for Azure Pipelines have the same environment as GitHub Actions (or perhaps it's GitHub Actions that's standing on the shoulders of Azure Pipelines)[1].
