System.Text.Json has many performance improvements in comparison to Newtonsoft.Json and System.Text.Json will continue to be developed and improved by the Microsoft team.
However, such migration will lead to problems for the projects that have already started using the SDK and especially its models because they will need to update their code as well and migrate to System.Text.Json. This issue is more like a suggestion if you aim for performance improvements.
System.Text.Json has many performance improvements in comparison to Newtonsoft.Json and System.Text.Json will continue to be developed and improved by the Microsoft team. However, such migration will lead to problems for the projects that have already started using the SDK and especially its models because they will need to update their code as well and migrate to System.Text.Json. This issue is more like a suggestion if you aim for performance improvements.